diff --git a/Source/Core/Windows/LinedefEditForm.cs b/Source/Core/Windows/LinedefEditForm.cs
index d28b1ef8..a3b2f611 100644
--- a/Source/Core/Windows/LinedefEditForm.cs
+++ b/Source/Core/Windows/LinedefEditForm.cs
@@ -46,8 +46,9 @@ namespace CodeImp.DoomBuilder.Windows
 		#region ================== Variables
 
 		private ICollection<Linedef> lines;
-		private List<LinedefProperties> linedefProps; //mxd
+		private List<LinedefProperties> linedefprops; //mxd
 		private bool preventchanges;
+		private bool undocreated; //mxd
 
 		//mxd. Window setup stuff
 		private static Point location = Point.Empty;
@@ -180,12 +181,7 @@ namespace CodeImp.DoomBuilder.Windows
 			// Keep this list
 			this.lines = lines;
 			if(lines.Count > 1) this.Text = "Edit Linedefs (" + lines.Count + ")";
-			linedefProps = new List<LinedefProperties>();
-
-			//mxd. Make undo
-			string undodesc = "linedef";
-			if(lines.Count > 1)	undodesc = lines.Count + " linedefs";
-			General.Map.UndoRedo.CreateUndo("Edit " + undodesc);
+			linedefprops = new List<LinedefProperties>();
 			
 			////////////////////////////////////////////////////////////////////////
 			// Set all options to the first linedef properties
@@ -354,7 +350,7 @@ namespace CodeImp.DoomBuilder.Windows
 				}
 
 				//mxd
-				linedefProps.Add(new LinedefProperties(l));
+				linedefprops.Add(new LinedefProperties(l));
 			}
 			
 			// Refresh controls so that they show their image
@@ -412,6 +408,16 @@ namespace CodeImp.DoomBuilder.Windows
 			}
 		}
 
+		//mxd
+		private void MakeUndo() 
+		{
+			if(undocreated) return;
+			undocreated = true;
+
+			//mxd. Make undo
+			General.Map.UndoRedo.CreateUndo("Edit " + (lines.Count > 1 ? lines.Count + " linedefs" : "linedef"));
+		}
+
 		//mxd
 		private void UpdateScriptControls()
 		{
@@ -446,6 +452,8 @@ namespace CodeImp.DoomBuilder.Windows
 				return;
 			}
 
+			MakeUndo(); //mxd
+
 			//mxd
 			bool hasAcs = !action.Empty && Array.IndexOf(GZBuilder.GZGeneral.ACS_SPECIALS, action.Value) != -1;
 			
@@ -557,7 +565,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void cancel_Click(object sender, EventArgs e)
 		{
 			//mxd. Let's pretend nothing of this really happened...
-			General.Map.UndoRedo.WithdrawUndo();
+			if(undocreated) General.Map.UndoRedo.WithdrawUndo();
 			
 			// Be gone
 			this.DialogResult = DialogResult.Cancel;
@@ -612,6 +620,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 			if(!preventchanges) 
 			{
+				MakeUndo(); //mxd
+				
 				// mxd. Apply action's default arguments 
 				if(showaction != 0) 
 				{
@@ -662,6 +672,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void flags_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
@@ -673,8 +684,8 @@ namespace CodeImp.DoomBuilder.Windows
 						l.SetFlag(c.Tag.ToString(), true);
 					else if(c.CheckState == CheckState.Unchecked)
 						l.SetFlag(c.Tag.ToString(), false);
-					else if(linedefProps[i].Flags.ContainsKey(c.Tag.ToString()))
-						l.SetFlag(c.Tag.ToString(), linedefProps[i].Flags[c.Tag.ToString()]);
+					else if(linedefprops[i].Flags.ContainsKey(c.Tag.ToString()))
+						l.SetFlag(c.Tag.ToString(), linedefprops[i].Flags[c.Tag.ToString()]);
 					else //linedefs created in the editor have empty Flags by default
 						l.SetFlag(c.Tag.ToString(), false);
 				}
@@ -693,6 +704,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void fronthigh_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(fronthigh.TextureName)) 
@@ -701,7 +713,7 @@ namespace CodeImp.DoomBuilder.Windows
 
 				foreach(Linedef l in lines) 
 				{
-					if(l.Front != null) l.Front.SetTextureHigh(linedefProps[i].Front != null ? linedefProps[i].Front.TextureTop : "-");
+					if(l.Front != null) l.Front.SetTextureHigh(linedefprops[i].Front != null ? linedefprops[i].Front.TextureTop : "-");
 					i++;
 				}
 			
@@ -722,6 +734,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void frontmid_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(frontmid.TextureName)) 
@@ -730,7 +743,7 @@ namespace CodeImp.DoomBuilder.Windows
 
 				foreach(Linedef l in lines) 
 				{
-					if(l.Front != null) l.Front.SetTextureMid(linedefProps[i].Front != null ? linedefProps[i].Front.TextureMid : "-");
+					if(l.Front != null) l.Front.SetTextureMid(linedefprops[i].Front != null ? linedefprops[i].Front.TextureMid : "-");
 					i++;
 				}
 			
@@ -751,6 +764,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void frontlow_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(frontlow.TextureName)) 
@@ -759,7 +773,7 @@ namespace CodeImp.DoomBuilder.Windows
 
 				foreach(Linedef l in lines) 
 				{
-					if(l.Front != null) l.Front.SetTextureLow(linedefProps[i].Front != null ? linedefProps[i].Front.TextureLow : "-");
+					if(l.Front != null) l.Front.SetTextureLow(linedefprops[i].Front != null ? linedefprops[i].Front.TextureLow : "-");
 					i++;
 				}
 			
@@ -780,6 +794,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void backhigh_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(backhigh.TextureName)) 
@@ -788,7 +803,7 @@ namespace CodeImp.DoomBuilder.Windows
 
 				foreach(Linedef l in lines) 
 				{
-					if(l.Back != null) l.Back.SetTextureHigh(linedefProps[i].Back != null ? linedefProps[i].Back.TextureTop : "-");
+					if(l.Back != null) l.Back.SetTextureHigh(linedefprops[i].Back != null ? linedefprops[i].Back.TextureTop : "-");
 					i++;
 				}
 			
@@ -809,6 +824,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void backmid_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(backmid.TextureName)) 
@@ -817,7 +833,7 @@ namespace CodeImp.DoomBuilder.Windows
 
 				foreach(Linedef l in lines) 
 				{
-					if(l.Back != null) l.Back.SetTextureMid(linedefProps[i].Back != null ? linedefProps[i].Back.TextureMid : "-");
+					if(l.Back != null) l.Back.SetTextureMid(linedefprops[i].Back != null ? linedefprops[i].Back.TextureMid : "-");
 					i++;
 				}
 			
@@ -838,6 +854,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void backlow_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(backlow.TextureName)) 
@@ -846,7 +863,7 @@ namespace CodeImp.DoomBuilder.Windows
 
 				foreach(Linedef l in lines) 
 				{
-					if(l.Back != null) l.Back.SetTextureLow(linedefProps[i].Back != null ? linedefProps[i].Back.TextureLow : "-");
+					if(l.Back != null) l.Back.SetTextureLow(linedefprops[i].Back != null ? linedefprops[i].Back.TextureLow : "-");
 					i++;
 				}
 			
@@ -867,17 +884,17 @@ namespace CodeImp.DoomBuilder.Windows
 		private void frontTextureOffset_OnValuesChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
-
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Front != null) 
 				{
-					if(linedefProps[i].Front != null) 
+					if(linedefprops[i].Front != null) 
 					{
-						l.Front.OffsetX = frontTextureOffset.GetValue1(linedefProps[i].Front.OffsetX);
-						l.Front.OffsetY = frontTextureOffset.GetValue2(linedefProps[i].Front.OffsetY);
+						l.Front.OffsetX = frontTextureOffset.GetValue1(linedefprops[i].Front.OffsetX);
+						l.Front.OffsetY = frontTextureOffset.GetValue2(linedefprops[i].Front.OffsetY);
 					} 
 					else 
 					{
@@ -897,17 +914,17 @@ namespace CodeImp.DoomBuilder.Windows
 		private void backTextureOffset_OnValuesChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
-
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Back != null) 
 				{
-					if(linedefProps[i].Back != null) 
+					if(linedefprops[i].Back != null) 
 					{
-						l.Back.OffsetX = backTextureOffset.GetValue1(linedefProps[i].Back.OffsetX);
-						l.Back.OffsetY = backTextureOffset.GetValue2(linedefProps[i].Back.OffsetY);
+						l.Back.OffsetX = backTextureOffset.GetValue1(linedefprops[i].Back.OffsetX);
+						l.Back.OffsetY = backTextureOffset.GetValue2(linedefprops[i].Back.OffsetY);
 					} 
 					else
 					{
diff --git a/Source/Core/Windows/LinedefEditFormUDMF.cs b/Source/Core/Windows/LinedefEditFormUDMF.cs
index 31f7b6eb..df30f077 100644
--- a/Source/Core/Windows/LinedefEditFormUDMF.cs
+++ b/Source/Core/Windows/LinedefEditFormUDMF.cs
@@ -48,8 +48,9 @@ namespace CodeImp.DoomBuilder.Windows
 		#region ================== Variables
 
 		private ICollection<Linedef> lines;
-		private List<LinedefProperties> linedefProps; //mxd
+		private List<LinedefProperties> linedefprops; //mxd
 		private bool preventchanges;
+		private bool undocreated; //mxd
 		private string arg0str; //mxd
 		private bool haveArg0Str; //mxd
 		private readonly string[] renderstyles; //mxd
@@ -265,12 +266,7 @@ namespace CodeImp.DoomBuilder.Windows
 			// Keep this list
 			this.lines = lines;
 			if(lines.Count > 1) this.Text = "Edit Linedefs (" + lines.Count + ")";
-			linedefProps = new List<LinedefProperties>();
-
-			//mxd. Make undo
-			string undodesc = "linedef";
-			if(lines.Count > 1)	undodesc = lines.Count + " linedefs";
-			General.Map.UndoRedo.CreateUndo("Edit " + undodesc);
+			linedefprops = new List<LinedefProperties>();
 			
 			////////////////////////////////////////////////////////////////////////
 			// Set all options to the first linedef properties
@@ -437,7 +433,6 @@ namespace CodeImp.DoomBuilder.Windows
 				}
 
 				// Custom fields
-				l.Fields.BeforeFieldsChange();
 				fieldslist.SetValues(l.Fields, false);
 
 				// Action/tags
@@ -516,7 +511,6 @@ namespace CodeImp.DoomBuilder.Windows
 						cbLightAbsoluteFront.CheckState = CheckState.Indeterminate;
 					}
 
-					l.Front.Fields.BeforeFieldsChange(); //mxd
 					frontTextureOffset.SetValues(l.Front.OffsetX, l.Front.OffsetY, false); //mxd
 				}
 
@@ -572,12 +566,11 @@ namespace CodeImp.DoomBuilder.Windows
 						cbLightAbsoluteBack.CheckState = CheckState.Indeterminate;
 					}
 
-					l.Back.Fields.BeforeFieldsChange(); //mxd
 					backTextureOffset.SetValues(l.Back.OffsetX, l.Back.OffsetY, false); //mxd
 				}
 
 				//mxd
-				linedefProps.Add(new LinedefProperties(l));
+				linedefprops.Add(new LinedefProperties(l));
 			}
 			
 			// Refresh controls so that they show their image
@@ -662,6 +655,26 @@ namespace CodeImp.DoomBuilder.Windows
 			}
 		}
 
+		//mxd
+		private void MakeUndo() 
+		{
+			if(undocreated) return;
+			undocreated = true;
+
+			//mxd. Make undo
+			General.Map.UndoRedo.CreateUndo("Edit " + (lines.Count > 1 ? lines.Count + " linedefs" : "linedef"));
+
+			if(General.Map.FormatInterface.HasCustomFields) 
+			{
+				foreach (Linedef l in lines)
+				{
+					l.Fields.BeforeFieldsChange();
+					if(l.Front != null) l.Front.Fields.BeforeFieldsChange();
+					if(l.Back != null) l.Back.Fields.BeforeFieldsChange();
+				}
+			}
+		}
+
 		//mxd
 		private void UpdateScriptControls() 
 		{
@@ -738,6 +751,8 @@ namespace CodeImp.DoomBuilder.Windows
 				return;
 			}
 
+			MakeUndo();
+
 			//mxd
 			bool hasAcs = !action.Empty && Array.IndexOf(GZBuilder.GZGeneral.ACS_SPECIALS, action.Value) != -1;
 			int locknumber = 0;
@@ -892,7 +907,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void cancel_Click(object sender, EventArgs e)
 		{
 			//mxd. Let's pretend nothing of this really happened...
-			General.Map.UndoRedo.WithdrawUndo();
+			if(undocreated) General.Map.UndoRedo.WithdrawUndo();
 			
 			// Be gone
 			this.DialogResult = DialogResult.Cancel;
@@ -949,6 +964,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 			if(!preventchanges) 
 			{
+				MakeUndo(); //mxd
+				
 				// mxd. Apply action's default arguments 
 				if(showaction != 0) 
 				{
@@ -1016,6 +1033,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void cbRenderStyle_SelectedIndexChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//update values
 			foreach(Linedef l in lines)
@@ -1028,13 +1046,14 @@ namespace CodeImp.DoomBuilder.Windows
 		private void alpha_WhenTextChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			//restore values
 			if(string.IsNullOrEmpty(alpha.Text)) 
 			{
 				foreach(Linedef l in lines) 
-					UDMFTools.SetFloat(l.Fields, "alpha", linedefProps[i++].Alpha, 1.0f);
+					UDMFTools.SetFloat(l.Fields, "alpha", linedefprops[i++].Alpha, 1.0f);
 			} 
 			else //update values
 			{
@@ -1052,6 +1071,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void flags_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
@@ -1063,8 +1083,8 @@ namespace CodeImp.DoomBuilder.Windows
 						l.SetFlag(c.Tag.ToString(), true);
 					else if(c.CheckState == CheckState.Unchecked)
 						l.SetFlag(c.Tag.ToString(), false);
-					else if(linedefProps[i].Flags.ContainsKey(c.Tag.ToString()))
-						l.SetFlag(c.Tag.ToString(), linedefProps[i].Flags[c.Tag.ToString()]);
+					else if(linedefprops[i].Flags.ContainsKey(c.Tag.ToString()))
+						l.SetFlag(c.Tag.ToString(), linedefprops[i].Flags[c.Tag.ToString()]);
 					else //linedefs created in the editor have empty Flags by default
 						l.SetFlag(c.Tag.ToString(), false);
 				}
@@ -1218,6 +1238,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void fronthigh_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(fronthigh.TextureName)) 
@@ -1226,7 +1247,7 @@ namespace CodeImp.DoomBuilder.Windows
 
 				foreach(Linedef l in lines) 
 				{
-					if(l.Front != null) l.Front.SetTextureHigh(linedefProps[i].Front != null ? linedefProps[i].Front.TextureTop : "-");
+					if(l.Front != null) l.Front.SetTextureHigh(linedefprops[i].Front != null ? linedefprops[i].Front.TextureTop : "-");
 					i++;
 				}
 			} 
@@ -1246,6 +1267,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void frontmid_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(frontmid.TextureName)) 
@@ -1254,7 +1276,7 @@ namespace CodeImp.DoomBuilder.Windows
 
 				foreach(Linedef l in lines) 
 				{
-					if(l.Front != null) l.Front.SetTextureMid(linedefProps[i].Front != null ? linedefProps[i].Front.TextureMid : "-");
+					if(l.Front != null) l.Front.SetTextureMid(linedefprops[i].Front != null ? linedefprops[i].Front.TextureMid : "-");
 					i++;
 				}
 			} 
@@ -1274,6 +1296,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void frontlow_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(frontlow.TextureName)) 
@@ -1282,7 +1305,7 @@ namespace CodeImp.DoomBuilder.Windows
 
 				foreach(Linedef l in lines) 
 				{
-					if(l.Front != null) l.Front.SetTextureLow(linedefProps[i].Front != null ? linedefProps[i].Front.TextureLow : "-");
+					if(l.Front != null) l.Front.SetTextureLow(linedefprops[i].Front != null ? linedefprops[i].Front.TextureLow : "-");
 					i++;
 				}
 			} 
@@ -1302,6 +1325,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void backhigh_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(backhigh.TextureName)) 
@@ -1310,7 +1334,7 @@ namespace CodeImp.DoomBuilder.Windows
 
 				foreach(Linedef l in lines) 
 				{
-					if(l.Back != null) l.Back.SetTextureHigh(linedefProps[i].Back != null ? linedefProps[i].Back.TextureTop : "-");
+					if(l.Back != null) l.Back.SetTextureHigh(linedefprops[i].Back != null ? linedefprops[i].Back.TextureTop : "-");
 					i++;
 				}
 			} 
@@ -1330,6 +1354,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void backmid_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(backmid.TextureName)) 
@@ -1338,7 +1363,7 @@ namespace CodeImp.DoomBuilder.Windows
 
 				foreach(Linedef l in lines) 
 				{
-					if(l.Back != null) l.Back.SetTextureMid(linedefProps[i].Back != null ? linedefProps[i].Back.TextureMid : "-");
+					if(l.Back != null) l.Back.SetTextureMid(linedefprops[i].Back != null ? linedefprops[i].Back.TextureMid : "-");
 					i++;
 				}
 			} 
@@ -1358,6 +1383,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void backlow_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(backlow.TextureName)) 
@@ -1366,7 +1392,7 @@ namespace CodeImp.DoomBuilder.Windows
 
 				foreach(Linedef l in lines) 
 				{
-					if(l.Back != null) l.Back.SetTextureLow(linedefProps[i].Back != null ? linedefProps[i].Back.TextureLow : "-");
+					if(l.Back != null) l.Back.SetTextureLow(linedefprops[i].Back != null ? linedefprops[i].Back.TextureLow : "-");
 					i++;
 				}
 			} 
@@ -1390,6 +1416,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void lightFront_WhenTextChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			//restore values
@@ -1398,7 +1425,7 @@ namespace CodeImp.DoomBuilder.Windows
 				foreach(Linedef l in lines) 
 				{
 					if(l.Front != null)
-						UDMFTools.SetInteger(l.Front.Fields, "light", (linedefProps[i].Front != null ? linedefProps[i].Front.Brightness : 0), 0);
+						UDMFTools.SetInteger(l.Front.Fields, "light", (linedefprops[i].Front != null ? linedefprops[i].Front.Brightness : 0), 0);
 					i++;
 				}
 			} 
@@ -1418,7 +1445,7 @@ namespace CodeImp.DoomBuilder.Windows
 							absolute = true;
 						}
 
-						int value = General.Clamp(lightFront.GetResult((linedefProps[i].Front != null ? linedefProps[i].Front.Brightness : 0)), (absolute ? 0 : -255), 255);
+						int value = General.Clamp(lightFront.GetResult((linedefprops[i].Front != null ? linedefprops[i].Front.Brightness : 0)), (absolute ? 0 : -255), 255);
 						UDMFTools.SetInteger(l.Front.Fields, "light", value, 0);
 					}
 					i++;
@@ -1432,6 +1459,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void lightBack_WhenTextChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			//restore values
@@ -1440,7 +1468,7 @@ namespace CodeImp.DoomBuilder.Windows
 				foreach(Linedef l in lines) 
 				{
 					if(l.Back != null)
-						UDMFTools.SetInteger(l.Back.Fields, "light", (linedefProps[i].Back != null ? linedefProps[i].Back.Brightness : 0), 0);
+						UDMFTools.SetInteger(l.Back.Fields, "light", (linedefprops[i].Back != null ? linedefprops[i].Back.Brightness : 0), 0);
 					i++;
 				}
 			} 
@@ -1460,7 +1488,7 @@ namespace CodeImp.DoomBuilder.Windows
 							absolute = true;
 						}
 
-						int value = General.Clamp(lightBack.GetResult((linedefProps[i].Back != null ? linedefProps[i].Back.Brightness : 0)), (absolute ? 0 : -255), 255);
+						int value = General.Clamp(lightBack.GetResult((linedefprops[i].Back != null ? linedefprops[i].Back.Brightness : 0)), (absolute ? 0 : -255), 255);
 						UDMFTools.SetInteger(l.Back.Fields, "light", value, 0);
 					}
 					i++;
@@ -1474,6 +1502,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void cbLightAbsoluteFront_CheckedChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			if(cbLightAbsoluteFront.Checked) 
 			{
@@ -1491,7 +1520,7 @@ namespace CodeImp.DoomBuilder.Windows
 				{
 					if(l.Front != null) 
 					{
-						if(linedefProps[i].Front != null && linedefProps[i].Front.AbsoluteBrightness) 
+						if(linedefprops[i].Front != null && linedefprops[i].Front.AbsoluteBrightness) 
 						{
 							l.Front.Fields["lightabsolute"] = new UniValue(UniversalType.Boolean, true);
 						} 
@@ -1519,6 +1548,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void cbLightAbsoluteBack_CheckedChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			if(cbLightAbsoluteBack.Checked) 
 			{
@@ -1536,7 +1566,7 @@ namespace CodeImp.DoomBuilder.Windows
 				{
 					if(l.Back != null) 
 					{
-						if(linedefProps[i].Back != null && linedefProps[i].Back.AbsoluteBrightness) 
+						if(linedefprops[i].Back != null && linedefprops[i].Back.AbsoluteBrightness) 
 						{
 							l.Back.Fields["lightabsolute"] = new UniValue(UniversalType.Boolean, true);
 						} 
@@ -1568,17 +1598,17 @@ namespace CodeImp.DoomBuilder.Windows
 		private void frontTextureOffset_OnValuesChanged(object sender, EventArgs e)
 		{
 			if(preventchanges) return;
-
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Front != null) 
 				{
-					if(linedefProps[i].Front != null) 
+					if(linedefprops[i].Front != null) 
 					{
-						l.Front.OffsetX = frontTextureOffset.GetValue1(linedefProps[i].Front.OffsetX);
-						l.Front.OffsetY = frontTextureOffset.GetValue2(linedefProps[i].Front.OffsetY);
+						l.Front.OffsetX = frontTextureOffset.GetValue1(linedefprops[i].Front.OffsetX);
+						l.Front.OffsetY = frontTextureOffset.GetValue2(linedefprops[i].Front.OffsetY);
 					} 
 					else 
 					{
@@ -1598,17 +1628,17 @@ namespace CodeImp.DoomBuilder.Windows
 		private void backTextureOffset_OnValuesChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
-
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Back != null) 
 				{
-					if(linedefProps[i].Back != null) 
+					if(linedefprops[i].Back != null) 
 					{
-						l.Back.OffsetX = backTextureOffset.GetValue1(linedefProps[i].Back.OffsetX);
-						l.Back.OffsetY = backTextureOffset.GetValue2(linedefProps[i].Back.OffsetY);
+						l.Back.OffsetX = backTextureOffset.GetValue1(linedefprops[i].Back.OffsetX);
+						l.Back.OffsetY = backTextureOffset.GetValue2(linedefprops[i].Back.OffsetY);
 					} 
 					else 
 					{
@@ -1632,14 +1662,15 @@ namespace CodeImp.DoomBuilder.Windows
 		private void pfcFrontOffsetTop_OnValuesChanged(object sender, EventArgs e)
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Front != null) 
 				{
-					float oldX = linedefProps[i].Front != null ? linedefProps[i].Front.OffsetTopX : 0f;
-					float oldY = linedefProps[i].Front != null ? linedefProps[i].Front.OffsetTopY : 0f;
+					float oldX = linedefprops[i].Front != null ? linedefprops[i].Front.OffsetTopX : 0f;
+					float oldY = linedefprops[i].Front != null ? linedefprops[i].Front.OffsetTopY : 0f;
 					pfcFrontOffsetTop.ApplyTo(l.Front.Fields, General.Map.FormatInterface.MinTextureOffset, General.Map.FormatInterface.MaxTextureOffset, oldX, oldY);
 				}
 				i++;
@@ -1653,14 +1684,15 @@ namespace CodeImp.DoomBuilder.Windows
 		private void pfcFrontOffsetMid_OnValuesChanged(object sender, EventArgs e)
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Front != null) 
 				{
-					float oldX = linedefProps[i].Front != null ? linedefProps[i].Front.OffsetMidX : 0f;
-					float oldY = linedefProps[i].Front != null ? linedefProps[i].Front.OffsetMidY : 0f;
+					float oldX = linedefprops[i].Front != null ? linedefprops[i].Front.OffsetMidX : 0f;
+					float oldY = linedefprops[i].Front != null ? linedefprops[i].Front.OffsetMidY : 0f;
 					pfcFrontOffsetMid.ApplyTo(l.Front.Fields, General.Map.FormatInterface.MinTextureOffset, General.Map.FormatInterface.MaxTextureOffset, oldX, oldY);
 				}
 
@@ -1675,14 +1707,15 @@ namespace CodeImp.DoomBuilder.Windows
 		private void pfcFrontOffsetBottom_OnValuesChanged(object sender, EventArgs e)
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Front != null) 
 				{
-					float oldX = linedefProps[i].Front != null ? linedefProps[i].Front.OffsetBottomX : 0f;
-					float oldY = linedefProps[i].Front != null ? linedefProps[i].Front.OffsetBottomY : 0f;
+					float oldX = linedefprops[i].Front != null ? linedefprops[i].Front.OffsetBottomX : 0f;
+					float oldY = linedefprops[i].Front != null ? linedefprops[i].Front.OffsetBottomY : 0f;
 					pfcFrontOffsetBottom.ApplyTo(l.Front.Fields, General.Map.FormatInterface.MinTextureOffset, General.Map.FormatInterface.MaxTextureOffset, oldX, oldY);
 				}
 
@@ -1697,14 +1730,15 @@ namespace CodeImp.DoomBuilder.Windows
 		private void pfcBackOffsetTop_OnValuesChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Back != null) 
 				{
-					float oldX = linedefProps[i].Back != null ? linedefProps[i].Back.OffsetTopX : 0f;
-					float oldY = linedefProps[i].Back != null ? linedefProps[i].Back.OffsetTopY : 0f;
+					float oldX = linedefprops[i].Back != null ? linedefprops[i].Back.OffsetTopX : 0f;
+					float oldY = linedefprops[i].Back != null ? linedefprops[i].Back.OffsetTopY : 0f;
 					pfcBackOffsetTop.ApplyTo(l.Back.Fields, General.Map.FormatInterface.MinTextureOffset, General.Map.FormatInterface.MaxTextureOffset, oldX, oldY);
 				}
 
@@ -1719,14 +1753,15 @@ namespace CodeImp.DoomBuilder.Windows
 		private void pfcBackOffsetMid_OnValuesChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Back != null) 
 				{
-					float oldX = linedefProps[i].Back != null ? linedefProps[i].Back.OffsetMidX : 0f;
-					float oldY = linedefProps[i].Back != null ? linedefProps[i].Back.OffsetMidY : 0f;
+					float oldX = linedefprops[i].Back != null ? linedefprops[i].Back.OffsetMidX : 0f;
+					float oldY = linedefprops[i].Back != null ? linedefprops[i].Back.OffsetMidY : 0f;
 					pfcBackOffsetMid.ApplyTo(l.Back.Fields, General.Map.FormatInterface.MinTextureOffset, General.Map.FormatInterface.MaxTextureOffset, oldX, oldY);
 				}
 
@@ -1741,14 +1776,15 @@ namespace CodeImp.DoomBuilder.Windows
 		private void pfcBackOffsetBottom_OnValuesChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Back != null) 
 				{
-					float oldX = linedefProps[i].Back != null ? linedefProps[i].Back.OffsetBottomX : 0f;
-					float oldY = linedefProps[i].Back != null ? linedefProps[i].Back.OffsetBottomY : 0f;
+					float oldX = linedefprops[i].Back != null ? linedefprops[i].Back.OffsetBottomX : 0f;
+					float oldY = linedefprops[i].Back != null ? linedefprops[i].Back.OffsetBottomY : 0f;
 					pfcBackOffsetBottom.ApplyTo(l.Back.Fields, General.Map.FormatInterface.MinTextureOffset, General.Map.FormatInterface.MaxTextureOffset, oldX, oldY);
 				}
 
@@ -1767,14 +1803,15 @@ namespace CodeImp.DoomBuilder.Windows
 		private void pfcFrontScaleTop_OnValuesChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Front != null) 
 				{
-					float oldX = linedefProps[i].Front != null ? linedefProps[i].Front.ScaleTopX : 1.0f;
-					float oldY = linedefProps[i].Front != null ? linedefProps[i].Front.ScaleTopY : 1.0f;
+					float oldX = linedefprops[i].Front != null ? linedefprops[i].Front.ScaleTopX : 1.0f;
+					float oldY = linedefprops[i].Front != null ? linedefprops[i].Front.ScaleTopY : 1.0f;
 					pfcFrontScaleTop.ApplyTo(l.Front.Fields, General.Map.FormatInterface.MinTextureOffset, General.Map.FormatInterface.MaxTextureOffset, oldX, oldY);
 				}
 
@@ -1789,14 +1826,15 @@ namespace CodeImp.DoomBuilder.Windows
 		private void pfcFrontScaleMid_OnValuesChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Front != null) 
 				{
-					float oldX = linedefProps[i].Front != null ? linedefProps[i].Front.ScaleMidX : 1.0f;
-					float oldY = linedefProps[i].Front != null ? linedefProps[i].Front.ScaleMidY : 1.0f;
+					float oldX = linedefprops[i].Front != null ? linedefprops[i].Front.ScaleMidX : 1.0f;
+					float oldY = linedefprops[i].Front != null ? linedefprops[i].Front.ScaleMidY : 1.0f;
 					pfcFrontScaleMid.ApplyTo(l.Front.Fields, General.Map.FormatInterface.MinTextureOffset, General.Map.FormatInterface.MaxTextureOffset, oldX, oldY);
 				}
 
@@ -1811,14 +1849,15 @@ namespace CodeImp.DoomBuilder.Windows
 		private void pfcFrontScaleBottom_OnValuesChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Front != null) 
 				{
-					float oldX = linedefProps[i].Front != null ? linedefProps[i].Front.ScaleBottomX : 1.0f;
-					float oldY = linedefProps[i].Front != null ? linedefProps[i].Front.ScaleBottomY : 1.0f;
+					float oldX = linedefprops[i].Front != null ? linedefprops[i].Front.ScaleBottomX : 1.0f;
+					float oldY = linedefprops[i].Front != null ? linedefprops[i].Front.ScaleBottomY : 1.0f;
 					pfcFrontScaleBottom.ApplyTo(l.Front.Fields, General.Map.FormatInterface.MinTextureOffset, General.Map.FormatInterface.MaxTextureOffset, oldX, oldY);
 				}
 
@@ -1833,14 +1872,15 @@ namespace CodeImp.DoomBuilder.Windows
 		private void pfcBackScaleTop_OnValuesChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Back != null) 
 				{
-					float oldX = linedefProps[i].Back != null ? linedefProps[i].Back.ScaleTopX : 1.0f;
-					float oldY = linedefProps[i].Back != null ? linedefProps[i].Back.ScaleTopY : 1.0f;
+					float oldX = linedefprops[i].Back != null ? linedefprops[i].Back.ScaleTopX : 1.0f;
+					float oldY = linedefprops[i].Back != null ? linedefprops[i].Back.ScaleTopY : 1.0f;
 					pfcBackScaleTop.ApplyTo(l.Back.Fields, General.Map.FormatInterface.MinTextureOffset, General.Map.FormatInterface.MaxTextureOffset, oldX, oldY);
 				}
 
@@ -1855,14 +1895,15 @@ namespace CodeImp.DoomBuilder.Windows
 		private void pfcBackScaleMid_OnValuesChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Back != null) 
 				{
-					float oldX = linedefProps[i].Back != null ? linedefProps[i].Back.ScaleMidX : 1.0f;
-					float oldY = linedefProps[i].Back != null ? linedefProps[i].Back.ScaleMidY : 1.0f;
+					float oldX = linedefprops[i].Back != null ? linedefprops[i].Back.ScaleMidX : 1.0f;
+					float oldY = linedefprops[i].Back != null ? linedefprops[i].Back.ScaleMidY : 1.0f;
 					pfcBackScaleMid.ApplyTo(l.Back.Fields, General.Map.FormatInterface.MinTextureOffset, General.Map.FormatInterface.MaxTextureOffset, oldX, oldY);
 				}
 
@@ -1877,14 +1918,15 @@ namespace CodeImp.DoomBuilder.Windows
 		private void pfcBackScaleBottom_OnValuesChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
 			{
 				if(l.Back != null) 
 				{
-					float oldX = linedefProps[i].Back != null ? linedefProps[i].Back.ScaleBottomX : 1.0f;
-					float oldY = linedefProps[i].Back != null ? linedefProps[i].Back.ScaleBottomY : 1.0f;
+					float oldX = linedefprops[i].Back != null ? linedefprops[i].Back.ScaleBottomX : 1.0f;
+					float oldY = linedefprops[i].Back != null ? linedefprops[i].Back.ScaleBottomY : 1.0f;
 					pfcBackScaleBottom.ApplyTo(l.Back.Fields, General.Map.FormatInterface.MinTextureOffset, General.Map.FormatInterface.MaxTextureOffset, oldX, oldY);
 				}
 
@@ -1903,6 +1945,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void flagsFront_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
@@ -1916,8 +1959,8 @@ namespace CodeImp.DoomBuilder.Windows
 						l.Front.SetFlag(c.Tag.ToString(), true);
 					else if(c.CheckState == CheckState.Unchecked)
 						l.Front.SetFlag(c.Tag.ToString(), false);
-					else if(linedefProps[i].Front.Flags.ContainsKey(c.Tag.ToString()))
-						l.Front.SetFlag(c.Tag.ToString(), linedefProps[i].Front.Flags[c.Tag.ToString()]);
+					else if(linedefprops[i].Front.Flags.ContainsKey(c.Tag.ToString()))
+						l.Front.SetFlag(c.Tag.ToString(), linedefprops[i].Front.Flags[c.Tag.ToString()]);
 					else //linedefs created in the editor have empty Flags by default
 						l.Front.SetFlag(c.Tag.ToString(), false);
 				}
@@ -1932,6 +1975,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void flagsBack_OnValueChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach(Linedef l in lines) 
@@ -1945,8 +1989,8 @@ namespace CodeImp.DoomBuilder.Windows
 						l.Back.SetFlag(c.Tag.ToString(), true);
 					else if(c.CheckState == CheckState.Unchecked)
 						l.Back.SetFlag(c.Tag.ToString(), false);
-					else if(linedefProps[i].Back.Flags.ContainsKey(c.Tag.ToString()))
-						l.Back.SetFlag(c.Tag.ToString(), linedefProps[i].Back.Flags[c.Tag.ToString()]);
+					else if(linedefprops[i].Back.Flags.ContainsKey(c.Tag.ToString()))
+						l.Back.SetFlag(c.Tag.ToString(), linedefprops[i].Back.Flags[c.Tag.ToString()]);
 					else //linedefs created in the editor have empty Flags by default
 						l.Back.SetFlag(c.Tag.ToString(), false);
 				}
diff --git a/Source/Core/Windows/SectorEditForm.cs b/Source/Core/Windows/SectorEditForm.cs
index 1f7e1f62..83749823 100644
--- a/Source/Core/Windows/SectorEditForm.cs
+++ b/Source/Core/Windows/SectorEditForm.cs
@@ -38,8 +38,9 @@ namespace CodeImp.DoomBuilder.Windows
 		#region ================== Variables
 
 		private ICollection<Sector> sectors;
-		private List<SectorProperties> sectorProps; //mxd
-		private bool blockUpdate; //mxd
+		private List<SectorProperties> sectorprops; //mxd
+		private bool preventchanges; //mxd
+		private bool undocreated; //mxd
 
 		//mxd. Window setup stuff
 		private static Point location = Point.Empty;
@@ -98,17 +99,12 @@ namespace CodeImp.DoomBuilder.Windows
 		// This sets up the form to edit the given sectors
 		public void Setup(ICollection<Sector> sectors)
 		{
-			blockUpdate = true; //mxd
+			preventchanges = true; //mxd
 
 			// Keep this list
 			this.sectors = sectors;
 			if(sectors.Count > 1) this.Text = "Edit Sectors (" + sectors.Count + ")";
-			sectorProps = new List<SectorProperties>(); //mxd
-
-			//mxd. Make undo
-			string undodesc = "sector";
-			if(sectors.Count > 1) undodesc = sectors.Count + " sectors";
-			General.Map.UndoRedo.CreateUndo("Edit " + undodesc);
+			sectorprops = new List<SectorProperties>(); //mxd
 
 			//mxd. Set default height offset
 			heightoffset.Text = "0";
@@ -163,13 +159,23 @@ namespace CodeImp.DoomBuilder.Windows
 				if(s.Tag != sc.Tag)	tagSelector.ClearTag(); //mxd
 
 				//mxd. Store initial properties
-				sectorProps.Add(new SectorProperties(s));
+				sectorprops.Add(new SectorProperties(s));
 			}
 
 			// Show sector height
 			UpdateSectorHeight();
 
-			blockUpdate = false; //mxd
+			preventchanges = false; //mxd
+		}
+
+		//mxd
+		private void MakeUndo() 
+		{
+			if(undocreated) return;
+			undocreated = true;
+
+			//mxd. Make undo
+			General.Map.UndoRedo.CreateUndo("Edit " + (sectors.Count > 1 ? sectors.Count + " sectors" : "sector"));
 		}
 
 		// This updates the sector height field
@@ -201,8 +207,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 			if(index > -1) 
 			{
-				int fh = floorheight.GetResult(sectorProps[index].FloorHeight); //mxd
-				int ch = ceilingheight.GetResult(sectorProps[index].CeilHeight); //mxd
+				int fh = floorheight.GetResult(sectorprops[index].FloorHeight); //mxd
+				int ch = ceilingheight.GetResult(sectorprops[index].CeilHeight); //mxd
 				int height = ch - fh;
 				sectorheight.Text = height.ToString();
 				sectorheight.Visible = true;
@@ -225,13 +231,13 @@ namespace CodeImp.DoomBuilder.Windows
 			if(string.IsNullOrEmpty(ceilingheight.Text)) 
 			{
 				foreach(Sector s in sectors)
-					s.CeilHeight = sectorProps[i++].CeilHeight + offset;
+					s.CeilHeight = sectorprops[i++].CeilHeight + offset;
 
 			} 
 			else //update values
 			{
 				foreach(Sector s in sectors)
-					s.CeilHeight = ceilingheight.GetResult(sectorProps[i++].CeilHeight) + offset;
+					s.CeilHeight = ceilingheight.GetResult(sectorprops[i++].CeilHeight) + offset;
 			}
 		}
 
@@ -245,13 +251,13 @@ namespace CodeImp.DoomBuilder.Windows
 			if(string.IsNullOrEmpty(floorheight.Text)) 
 			{
 				foreach(Sector s in sectors)
-					s.FloorHeight = sectorProps[i++].FloorHeight + offset;
+					s.FloorHeight = sectorprops[i++].FloorHeight + offset;
 
 			} 
 			else //update values
 			{
 				foreach(Sector s in sectors)
-					s.FloorHeight = floorheight.GetResult(sectorProps[i++].FloorHeight) + offset;
+					s.FloorHeight = floorheight.GetResult(sectorprops[i++].FloorHeight) + offset;
 			}
 		}
 
@@ -278,6 +284,8 @@ namespace CodeImp.DoomBuilder.Windows
 				return;
 			}
 
+			MakeUndo(); //mxd
+
 			// Go for all sectors
 			int tagoffset = 0; //mxd
 			foreach(Sector s in sectors) 
@@ -300,7 +308,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void cancel_Click(object sender, EventArgs e)
 		{
 			//mxd. perform undo
-			General.Map.UndoRedo.WithdrawUndo();
+			if(undocreated) General.Map.UndoRedo.WithdrawUndo();
 			
 			// And be gone
 			this.DialogResult = DialogResult.Cancel;
@@ -334,7 +342,8 @@ namespace CodeImp.DoomBuilder.Windows
 		// Ceiling height changes
 		private void ceilingheight_TextChanged(object sender, EventArgs e)
 		{
-			if(blockUpdate) return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			UpdateCeilingHeight();
 			UpdateSectorHeight();
@@ -346,7 +355,8 @@ namespace CodeImp.DoomBuilder.Windows
 		// Floor height changes
 		private void floorheight_TextChanged(object sender, EventArgs e)
 		{
-			if(blockUpdate) return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			UpdateFloorHeight();
 			UpdateSectorHeight();
@@ -358,7 +368,8 @@ namespace CodeImp.DoomBuilder.Windows
 		// Height offset changes
 		private void heightoffset_WhenTextChanged(object sender, EventArgs e) 
 		{
-			if(blockUpdate) return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			UpdateFloorHeight();
 			UpdateCeilingHeight();
@@ -370,13 +381,14 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void floortex_OnValueChanged(object sender, EventArgs e) 
 		{
-			if(blockUpdate) return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(floortex.TextureName)) 
 			{
 				int i = 0;
-				foreach(Sector s in sectors) s.SetFloorTexture(sectorProps[i++].FloorTexture);
+				foreach(Sector s in sectors) s.SetFloorTexture(sectorprops[i++].FloorTexture);
 			
 			} 
 			else //update values
@@ -393,13 +405,14 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void ceilingtex_OnValueChanged(object sender, EventArgs e) 
 		{
-			if(blockUpdate) return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(ceilingtex.TextureName)) 
 			{
 				int i = 0;
-				foreach(Sector s in sectors) s.SetCeilTexture(sectorProps[i++].CeilTexture);
+				foreach(Sector s in sectors) s.SetCeilTexture(sectorprops[i++].CeilTexture);
 			
 			} 
 			else //update values
@@ -416,19 +429,20 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void brightness_WhenTextChanged(object sender, EventArgs e) 
 		{
-			if(blockUpdate) return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			//restore values
 			if(string.IsNullOrEmpty(brightness.Text)) 
 			{
-				foreach(Sector s in sectors) s.Brightness = sectorProps[i++].Brightness;
+				foreach(Sector s in sectors) s.Brightness = sectorprops[i++].Brightness;
 			
 			} 
 			else //update values
 			{
 				foreach(Sector s in sectors)
-					s.Brightness = General.Clamp(brightness.GetResult(sectorProps[i++].Brightness), General.Map.FormatInterface.MinBrightness, General.Map.FormatInterface.MaxBrightness);
+					s.Brightness = General.Clamp(brightness.GetResult(sectorprops[i++].Brightness), General.Map.FormatInterface.MinBrightness, General.Map.FormatInterface.MaxBrightness);
 			}
 
 			General.Map.IsChanged = true;
diff --git a/Source/Core/Windows/SectorEditFormUDMF.cs b/Source/Core/Windows/SectorEditFormUDMF.cs
index 8f1b0d13..cbde492f 100644
--- a/Source/Core/Windows/SectorEditFormUDMF.cs
+++ b/Source/Core/Windows/SectorEditFormUDMF.cs
@@ -26,7 +26,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private ICollection<Sector> sectors;
 		private Dictionary<Sector, SectorProperties> sectorprops; //mxd
-		private bool blockupdate; //mxd
+		private bool preventchanges; //mxd
+		private bool undocreated; //mxd
 		private StepsList anglesteps; //mxd
 		private readonly string[] renderstyles; //mxd
 
@@ -232,18 +233,13 @@ namespace CodeImp.DoomBuilder.Windows
 		// This sets up the form to edit the given sectors
 		public void Setup(ICollection<Sector> sectors) 
 		{
-			blockupdate = true; //mxd
+			preventchanges = true; //mxd
 
 			// Keep this list
 			this.sectors = sectors;
 			if(sectors.Count > 1) this.Text = "Edit Sectors (" + sectors.Count + ")";
 			sectorprops = new Dictionary<Sector, SectorProperties>(sectors.Count); //mxd
 
-			//mxd. Make undo
-			string undodesc = "sector";
-			if(sectors.Count > 1) undodesc = sectors.Count + " sectors";
-			General.Map.UndoRedo.CreateUndo("Edit " + undodesc);
-
 			//mxd. Set default height offset
 			heightoffset.Text = "0";
 
@@ -424,7 +420,6 @@ namespace CodeImp.DoomBuilder.Windows
 				if(s.Tag != sc.Tag) tagSelector.ClearTag(); //mxd
 
 				// Custom fields
-				s.Fields.BeforeFieldsChange(); //mxd
 				fieldslist.SetValues(s.Fields, false);
 
 				//mxd. Angle steps
@@ -460,7 +455,18 @@ namespace CodeImp.DoomBuilder.Windows
 			if(useCeilSlopeLineAngles) ceilingslopecontrol.StepValues = anglesteps;
 			if(useFloorSlopeLineAngles) floorslopecontrol.StepValues = anglesteps;
 
-			blockupdate = false; //mxd
+			preventchanges = false; //mxd
+		}
+
+		//mxd
+		private void MakeUndo() 
+		{
+			if(undocreated) return;
+			undocreated = true;
+
+			//mxd. Make undo
+			General.Map.UndoRedo.CreateUndo("Edit " + (sectors.Count > 1 ? sectors.Count + " sectors" : "sector"));
+			foreach(Sector s in sectors) s.Fields.BeforeFieldsChange();
 		}
 
 		// mxd
@@ -611,6 +617,8 @@ namespace CodeImp.DoomBuilder.Windows
 				General.Map.Config.SectorRenderStyles.Keys.CopyTo(rskeys, 0);
 			}
 
+			MakeUndo(); //mxd
+
 			// Go for all sectors
 			int tagoffset = 0; //mxd
 			foreach(Sector s in sectors) 
@@ -705,7 +713,7 @@ namespace CodeImp.DoomBuilder.Windows
 		private void cancel_Click(object sender, EventArgs e) 
 		{
 			//mxd. Let's pretend nothing of this really happened...
-			General.Map.UndoRedo.WithdrawUndo();
+			if(undocreated) General.Map.UndoRedo.WithdrawUndo();
 			
 			// Be gone
 			this.DialogResult = DialogResult.Cancel;
@@ -763,7 +771,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void ceilingheight_WhenTextChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges)	return;
+			MakeUndo(); //mxd
 
 			UpdateCeilingHeight();
 			UpdateSectorHeight();
@@ -774,7 +783,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void floorheight_WhenTextChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges)	return;
+			MakeUndo(); //mxd
 
 			UpdateFloorHeight();
 			UpdateSectorHeight();
@@ -785,7 +795,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void heightoffset_WhenTextChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate) return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			UpdateFloorHeight();
 			UpdateCeilingHeight();
@@ -797,7 +808,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void brightness_WhenTextChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges)	return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(brightness.Text)) 
@@ -818,7 +830,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void ceilingtex_OnValueChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges)	return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(ceilingtex.TextureName)) 
@@ -842,7 +855,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void floortex_OnValueChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges)	return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(floortex.TextureName)) 
@@ -866,7 +880,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void floorRotation_WhenTextChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges)	return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(floorRotation.Text))
@@ -896,7 +911,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void ceilRotation_WhenTextChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(ceilRotation.Text))
@@ -926,7 +942,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void lightColor_OnValueChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			foreach(Sector s in sectors) 
 			{
@@ -940,7 +957,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void fadeColor_OnValueChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			foreach(Sector s in sectors) 
 			{
@@ -958,7 +976,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void ceilOffsets_OnValuesChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			foreach(Sector s in sectors) 
 			{
@@ -973,7 +992,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void floorOffsets_OnValuesChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			foreach(Sector s in sectors) 
 			{
@@ -988,7 +1008,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void ceilScale_OnValuesChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			foreach(Sector s in sectors) 
 			{
@@ -1003,7 +1024,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void floorScale_OnValuesChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			foreach(Sector s in sectors) 
 			{
@@ -1018,7 +1040,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void ceilBrightness_WhenTextChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(ceilBrightness.Text)) 
@@ -1055,7 +1078,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void floorBrightness_WhenTextChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			//restore values
 			if(string.IsNullOrEmpty(floorBrightness.Text)) 
@@ -1092,7 +1116,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void ceilLightAbsolute_CheckedChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			if(ceilLightAbsolute.Checked) 
 			{
@@ -1136,7 +1161,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void floorLightAbsolute_CheckedChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate)	return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 
 			if(floorLightAbsolute.Checked)
 			{
@@ -1287,7 +1313,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void ceilingslopecontrol_OnAnglesChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate) return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 			float anglexy, anglez;
 
 			//Set or restore values
@@ -1312,7 +1339,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void floorslopecontrol_OnAnglesChanged(object sender, EventArgs e) 
 		{
-			if(blockupdate) return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 			float anglexy, anglez;
 
 			//Set or restore values
@@ -1338,6 +1366,7 @@ namespace CodeImp.DoomBuilder.Windows
 		// Update displayed ceiling offset value
 		private void ceilingslopecontrol_OnPivotModeChanged(object sender, EventArgs e) 
 		{
+			MakeUndo(); //mxd
 			bool first = true;
 			foreach (Sector s in sectors)
 			{
@@ -1349,6 +1378,7 @@ namespace CodeImp.DoomBuilder.Windows
 		// Update displayed floor offset value
 		private void floorslopecontrol_OnPivotModeChanged(object sender, EventArgs e) 
 		{
+			MakeUndo(); //mxd
 			bool first = true;
 			foreach (Sector s in sectors)
 			{
@@ -1359,6 +1389,7 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void ceilingslopecontrol_OnResetClicked(object sender, EventArgs e) 
 		{
+			MakeUndo(); //mxd
 			ceilingslopecontrol.SetOffset(General.GetByIndex(sectors, 0).CeilHeight, true);
 			
 			foreach(Sector s in sectors) 
@@ -1378,6 +1409,7 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void floorslopecontrol_OnResetClicked(object sender, EventArgs e) 
 		{
+			MakeUndo(); //mxd
 			floorslopecontrol.SetOffset(General.GetByIndex(sectors, 0).FloorHeight, true);
 			
 			foreach(Sector s in sectors) 
diff --git a/Source/Core/Windows/ThingEditForm.cs b/Source/Core/Windows/ThingEditForm.cs
index 3688d138..8b44e29e 100644
--- a/Source/Core/Windows/ThingEditForm.cs
+++ b/Source/Core/Windows/ThingEditForm.cs
@@ -47,9 +47,10 @@ namespace CodeImp.DoomBuilder.Windows
 		private ICollection<Thing> things;
 		private ThingTypeInfo thinginfo;
 		private bool preventchanges;
-		//mxd
-		private static bool useAbsoluteHeight;
-		private List<ThingProperties> thingProps; //mxd
+		private bool preventmapchange; //mxd
+		private bool undocreated; //mxd
+		private static bool useAbsoluteHeight; //mxd
+		private List<ThingProperties> thingprops; //mxd
 
 		//mxd. Window setup stuff
 		private static Point location = Point.Empty;
@@ -149,11 +150,6 @@ namespace CodeImp.DoomBuilder.Windows
 			hint.Visible = things.Count > 1; //mxd
 			hintlabel.Visible = things.Count > 1; //mxd
 			thingtype.UseMultiSelection = things.Count > 1; //mxd
-
-			//mxd. Make undo
-			string undodesc = "thing";
-			if(things.Count > 1) undodesc = things.Count + " things";
-			General.Map.UndoRedo.CreateUndo("Edit " + undodesc);
 			
 			////////////////////////////////////////////////////////////////////////
 			// Set all options to the first thing properties
@@ -200,7 +196,7 @@ namespace CodeImp.DoomBuilder.Windows
 			// Now go for all lines and change the options when a setting is different
 			////////////////////////////////////////////////////////////////////////
 
-			thingProps = new List<ThingProperties>();
+			thingprops = new List<ThingProperties>();
 
 			// Go for all things
 			foreach(Thing t in things)
@@ -250,14 +246,16 @@ namespace CodeImp.DoomBuilder.Windows
 				if(t.Args[4] != arg4.GetResult(-1)) arg4.ClearValue();
 
 				//mxd. Store initial properties
-				thingProps.Add(new ThingProperties(t));
+				thingprops.Add(new ThingProperties(t));
 			}
 
 			preventchanges = false;
 
 			//mxd. Trigger updates manually...
+			preventmapchange = true;
 			angle_WhenTextChanged(angle, EventArgs.Empty);
 			flags_OnValueChanged(flags, EventArgs.Empty);
+			preventmapchange = false;
 
 			UpdateScriptControls(); //mxd
 			actionhelp.UpdateAction(action.GetValue()); //mxd
@@ -294,6 +292,16 @@ namespace CodeImp.DoomBuilder.Windows
 			}
 		}
 
+		//mxd
+		private void MakeUndo() 
+		{
+			if(undocreated) return;
+			undocreated = true;
+
+			//mxd. Make undo
+			General.Map.UndoRedo.CreateUndo("Edit " + (things.Count > 1 ? things.Count + " things" : "thing"));
+		}
+
 		//mxd
 		private void UpdateScriptControls() 
 		{
@@ -345,6 +353,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 			if(!preventchanges)
 			{
+				MakeUndo();
+				
 				// mxd. Apply action's or thing's default arguments
 				if (showaction != 0 || thinginfo != null) 
 				{
@@ -382,7 +392,7 @@ namespace CodeImp.DoomBuilder.Windows
 			preventchanges = true;
 			anglecontrol.Angle = angle.GetResult(GZBuilder.Controls.AngleControl.NO_ANGLE);
 			preventchanges = false;
-			UpdateAngle(); //mxd
+			if(!preventmapchange) ApplyAngleChange(); //mxd
 		}
 
 		//mxd. Angle control clicked
@@ -390,12 +400,14 @@ namespace CodeImp.DoomBuilder.Windows
 		{
 			if(preventchanges) return;
 			angle.Text = anglecontrol.Angle.ToString();
-			UpdateAngle();
+			if(!preventmapchange) ApplyAngleChange();
 		}
 
 		// Apply clicked
 		private void apply_Click(object sender, EventArgs e)
 		{
+			MakeUndo();
+			
 			List<string> defaultflags = new List<string>();
 
 			// Verify the tag
@@ -500,8 +512,8 @@ namespace CodeImp.DoomBuilder.Windows
 		// Cancel clicked
 		private void cancel_Click(object sender, EventArgs e)
 		{
-			//mxd. perform undo
-			General.Map.UndoRedo.WithdrawUndo();
+			//mxd. Perform undo?
+			if(undocreated) General.Map.UndoRedo.WithdrawUndo();
 			
 			// Be gone
 			this.DialogResult = DialogResult.Cancel;
@@ -512,6 +524,8 @@ namespace CodeImp.DoomBuilder.Windows
 		private void cbAbsoluteHeight_CheckedChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
+
 			useAbsoluteHeight = cbAbsoluteHeight.Checked;
 			zlabel.Text = (useAbsoluteHeight ? "Abs. Z:" : "Z:");
 			
@@ -565,11 +579,12 @@ namespace CodeImp.DoomBuilder.Windows
 		private void posX_WhenTextChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			// Update values
 			foreach(Thing t in things)
-				t.Move(new Vector2D(posX.GetResultFloat(thingProps[i++].X), t.Position.y));
+				t.Move(new Vector2D(posX.GetResultFloat(thingprops[i++].X), t.Position.y));
 
 			General.Map.IsChanged = true;
 			if(OnValuesChanged != null)	OnValuesChanged(this, EventArgs.Empty);
@@ -578,11 +593,12 @@ namespace CodeImp.DoomBuilder.Windows
 		private void posY_WhenTextChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			// Update values
 			foreach(Thing t in things)
-				t.Move(new Vector2D(t.Position.x, posY.GetResultFloat(thingProps[i++].Y)));
+				t.Move(new Vector2D(t.Position.x, posY.GetResultFloat(thingprops[i++].Y)));
 
 			General.Map.IsChanged = true;
 			if(OnValuesChanged != null) OnValuesChanged(this, EventArgs.Empty);
@@ -591,20 +607,21 @@ namespace CodeImp.DoomBuilder.Windows
 		private void posZ_WhenTextChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			if(string.IsNullOrEmpty(posZ.Text)) 
 			{
 				// Restore values
 				foreach(Thing t in things)
-					t.Move(new Vector3D(t.Position.x, t.Position.y, thingProps[i++].Z));
+					t.Move(new Vector3D(t.Position.x, t.Position.y, thingprops[i++].Z));
 			} 
 			else 
 			{ 
 				// Update values
 				foreach(Thing t in things) 
 				{
-					float z = posZ.GetResultFloat(thingProps[i++].Z);
+					float z = posZ.GetResultFloat(thingprops[i++].Z);
 					if(useAbsoluteHeight && !posZ.CheckIsRelative() && t.Sector != null)
 						z -= t.Sector.FloorHeight;
 					t.Move(new Vector3D(t.Position.x, t.Position.y, z));
@@ -625,6 +642,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 			//mxd. Update things
 			if(preventchanges) return;
+			MakeUndo(); //mxd
+
 			if(((thingtype.GetResult(0) < General.Map.FormatInterface.MinThingType) || (thingtype.GetResult(0) > General.Map.FormatInterface.MaxThingType)))
 				return;
 
@@ -642,9 +661,10 @@ namespace CodeImp.DoomBuilder.Windows
 		}
 
 		//mxd
-		private void UpdateAngle() 
+		private void ApplyAngleChange() 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			//restore values
@@ -652,13 +672,13 @@ namespace CodeImp.DoomBuilder.Windows
 			{
 				// Apply rotation
 				foreach(Thing t in things)
-					t.Rotate(thingProps[i++].AngleDoom);
-			} 
-			else 
-			{ //update values
+					t.Rotate(thingprops[i++].AngleDoom);
+			}
+			else //update values
+			{ 
 				// Apply rotation
 				foreach(Thing t in things)
-					t.Rotate(angle.GetResult(thingProps[i++].AngleDoom));
+					t.Rotate(angle.GetResult(thingprops[i++].AngleDoom));
 			}
 
 			General.Map.IsChanged = true;
diff --git a/Source/Core/Windows/ThingEditFormUDMF.cs b/Source/Core/Windows/ThingEditFormUDMF.cs
index c603fb2b..f4a5f8ff 100644
--- a/Source/Core/Windows/ThingEditFormUDMF.cs
+++ b/Source/Core/Windows/ThingEditFormUDMF.cs
@@ -48,10 +48,12 @@ namespace CodeImp.DoomBuilder.Windows
 		private ICollection<Thing> things;
 		private ThingTypeInfo thinginfo;
 		private bool preventchanges;
+		private bool preventmapchange; //mxd
+		private bool undocreated; //mxd
 		private static bool useAbsoluteHeight;
 		private string arg0str;
 		private bool haveArg0Str;
-		private List<ThingProperties> thingProps; //mxd
+		private List<ThingProperties> thingprops; //mxd
 		private readonly string[] renderstyles; //mxd
 
 		//mxd. Window setup stuff
@@ -173,11 +175,6 @@ namespace CodeImp.DoomBuilder.Windows
 			hintlabel.Visible = things.Count > 1; //mxd
 			thingtype.UseMultiSelection = things.Count > 1; //mxd
 
-			//mxd. Make undo
-			string undodesc = "thing";
-			if(things.Count > 1) undodesc = things.Count + " things";
-			General.Map.UndoRedo.CreateUndo("Edit " + undodesc);
-
 			////////////////////////////////////////////////////////////////////////
 			// Set all options to the first thing properties
 			////////////////////////////////////////////////////////////////////////
@@ -237,7 +234,7 @@ namespace CodeImp.DoomBuilder.Windows
 			// Now go for all lines and change the options when a setting is different
 			////////////////////////////////////////////////////////////////////////
 
-			thingProps = new List<ThingProperties>();
+			thingprops = new List<ThingProperties>();
 
 			// Go for all things
 			foreach(Thing t in things) 
@@ -285,7 +282,6 @@ namespace CodeImp.DoomBuilder.Windows
 				if(t.Args[4] != arg4.GetResult(-1)) arg4.ClearValue();
 
 				//mxd. Custom fields
-				t.Fields.BeforeFieldsChange(); //mxd
 				fieldslist.SetValues(t.Fields, false);
 				if (t.Fields.GetValue("conversation", 0).ToString() != conversationID.Text) conversationID.Text = "";
 				if (t.Fields.GetValue("gravity", 1.0f).ToString() != gravity.Text) gravity.Text = "";
@@ -310,7 +306,7 @@ namespace CodeImp.DoomBuilder.Windows
 				}
 
 				//mxd. Store initial properties
-				thingProps.Add(new ThingProperties(t));
+				thingprops.Add(new ThingProperties(t));
 
 				//mxd. add user vars
 				/*if(info != null && info.Actor != null && info.Actor.UserVars.Count > 0) 
@@ -326,10 +322,12 @@ namespace CodeImp.DoomBuilder.Windows
 			preventchanges = false;
 
 			//mxd. Trigger updates manually...
+			preventmapchange = true;
 			angle_WhenTextChanged(angle, EventArgs.Empty);
 			pitch_WhenTextChanged(pitch, EventArgs.Empty);
 			roll_WhenTextChanged(roll, EventArgs.Empty);
 			flags_OnValueChanged(flags, EventArgs.Empty);
+			preventmapchange = false;
 
 			UpdateScriptControls(); //mxd
 			actionhelp.UpdateAction(action.GetValue()); //mxd
@@ -375,6 +373,17 @@ namespace CodeImp.DoomBuilder.Windows
 			}
 		}
 
+		//mxd
+		private void MakeUndo() 
+		{
+			if(undocreated) return;
+			undocreated = true;
+
+			//mxd. Make undo
+			General.Map.UndoRedo.CreateUndo("Edit " + (things.Count > 1 ? things.Count + " things" : "thing"));
+			foreach(Thing t in things) t.Fields.BeforeFieldsChange();
+		}
+
 		//mxd
 		private void UpdateScriptControls() 
 		{
@@ -440,6 +449,8 @@ namespace CodeImp.DoomBuilder.Windows
 
 			if(!preventchanges) 
 			{
+				MakeUndo(); //mxd
+				
 				// mxd. Apply action's or thing's default arguments
 				if(showaction != 0 || thinginfo != null) 
 				{
@@ -477,7 +488,7 @@ namespace CodeImp.DoomBuilder.Windows
 			preventchanges = true;
 			anglecontrol.Angle = angle.GetResult(GZBuilder.Controls.AngleControl.NO_ANGLE);
 			preventchanges = false;
-			UpdateAngle(); //mxd
+			if(!preventmapchange) ApplyAngleChange(); //mxd
 		}
 
 		//mxd. Angle control clicked
@@ -485,7 +496,7 @@ namespace CodeImp.DoomBuilder.Windows
 		{
 			if(preventchanges) return;
 			angle.Text = anglecontrol.Angle.ToString();
-			UpdateAngle();
+			if(!preventmapchange) ApplyAngleChange();
 		}
 
 		private void pitch_WhenTextChanged(object sender, EventArgs e) 
@@ -495,14 +506,14 @@ namespace CodeImp.DoomBuilder.Windows
 			preventchanges = true;
 			pitchControl.Angle = (p == GZBuilder.Controls.AngleControl.NO_ANGLE ? p : p + 90);
 			preventchanges = false;
-			UpdatePitch();
+			if(!preventmapchange) ApplyPitchChange();
 		}
 
 		private void pitchControl_AngleChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
 			pitch.Text = (General.ClampAngle(pitchControl.Angle - 90)).ToString();
-			UpdatePitch();
+			if(!preventmapchange) ApplyPitchChange();
 		}
 
 		private void roll_WhenTextChanged(object sender, EventArgs e) 
@@ -512,19 +523,22 @@ namespace CodeImp.DoomBuilder.Windows
 			preventchanges = true;
 			rollControl.Angle = (r == GZBuilder.Controls.AngleControl.NO_ANGLE ? r : r + 90);
 			preventchanges = false;
-			UpdateRoll();
+			if(!preventmapchange) ApplyRollChange();
 		}
 
 		private void rollControl_AngleChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
 			roll.Text = (General.ClampAngle(rollControl.Angle - 90)).ToString();
-			UpdateRoll();
+			if(!preventmapchange) ApplyRollChange();
 		}
 
 		// Apply clicked
 		private void apply_Click(object sender, EventArgs e) 
 		{
+			// Make Undo
+			MakeUndo(); //mxd
+			
 			List<string> defaultflags = new List<string>();
 
 			// Verify the tag
@@ -664,8 +678,8 @@ namespace CodeImp.DoomBuilder.Windows
 		// Cancel clicked
 		private void cancel_Click(object sender, EventArgs e) 
 		{
-			//mxd. perform undo
-			General.Map.UndoRedo.WithdrawUndo();
+			//mxd. Perform undo?
+			if(undocreated) General.Map.UndoRedo.WithdrawUndo();
 
 			// Be gone
 			this.DialogResult = DialogResult.Cancel;
@@ -685,6 +699,8 @@ namespace CodeImp.DoomBuilder.Windows
 		private void cbAbsoluteHeight_CheckedChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
+
 			useAbsoluteHeight = cbAbsoluteHeight.Checked;
 			zlabel.Text = useAbsoluteHeight ? "Abs. Z:" : "Z:";
 
@@ -737,11 +753,12 @@ namespace CodeImp.DoomBuilder.Windows
 		private void posX_WhenTextChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			// Update values
 			foreach(Thing t in things)
-				t.Move(new Vector2D(posX.GetResultFloat(thingProps[i++].X), t.Position.y));
+				t.Move(new Vector2D(posX.GetResultFloat(thingprops[i++].X), t.Position.y));
 
 			General.Map.IsChanged = true;
 			if(OnValuesChanged != null) OnValuesChanged(this, EventArgs.Empty);
@@ -750,11 +767,12 @@ namespace CodeImp.DoomBuilder.Windows
 		private void posY_WhenTextChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			// Update values
 			foreach(Thing t in things)
-				t.Move(new Vector2D(t.Position.x, posY.GetResultFloat(thingProps[i++].Y)));
+				t.Move(new Vector2D(t.Position.x, posY.GetResultFloat(thingprops[i++].Y)));
 
 			General.Map.IsChanged = true;
 			if(OnValuesChanged != null) OnValuesChanged(this, EventArgs.Empty);
@@ -763,20 +781,21 @@ namespace CodeImp.DoomBuilder.Windows
 		private void posZ_WhenTextChanged(object sender, EventArgs e) 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			if(string.IsNullOrEmpty(posZ.Text)) 
 			{
 				// Restore values
 				foreach(Thing t in things)
-					t.Move(new Vector3D(t.Position.x, t.Position.y, thingProps[i++].Z));
+					t.Move(new Vector3D(t.Position.x, t.Position.y, thingprops[i++].Z));
 			} 
 			else 
 			{
 				// Update values
 				foreach(Thing t in things) 
 				{
-					float z = posZ.GetResultFloat(thingProps[i++].Z);
+					float z = posZ.GetResultFloat(thingprops[i++].Z);
 					if(useAbsoluteHeight && !posZ.CheckIsRelative() && t.Sector != null)
 						z -= t.Sector.FloorHeight;
 					t.Move(new Vector3D(t.Position.x, t.Position.y, z));
@@ -789,13 +808,14 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void scale_OnValuesChanged(object sender, EventArgs e) 
 		{
-			if (preventchanges) return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			foreach (Thing t in things)
 			{
-				float sx = scale.GetValue1(thingProps[i].ScaleX);
-				float sy = scale.GetValue2(thingProps[i].ScaleY);
+				float sx = scale.GetValue1(thingprops[i].ScaleX);
+				float sy = scale.GetValue2(thingprops[i].ScaleY);
 				t.SetScale((sx == 0 ? 1.0f : sx), (sy == 0 ? 1.0f : sy));
 				i++;
 			}
@@ -819,6 +839,8 @@ namespace CodeImp.DoomBuilder.Windows
 					|| (thingtype.GetResult(0) > General.Map.FormatInterface.MaxThingType))
 				return;
 
+			MakeUndo(); //mxd
+
 			foreach(Thing t in things) 
 			{
 				//Set type
@@ -833,61 +855,64 @@ namespace CodeImp.DoomBuilder.Windows
 		}
 
 		//mxd
-		private void UpdateAngle() 
+		private void ApplyAngleChange() 
 		{
 			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			//restore values
 			if(string.IsNullOrEmpty(angle.Text)) 
 			{
-				foreach(Thing t in things) t.Rotate(thingProps[i++].AngleDoom);
+				foreach(Thing t in things) t.Rotate(thingprops[i++].AngleDoom);
 			} 
 			else //update values
 			{
 				foreach(Thing t in things)
-					t.Rotate(angle.GetResult(thingProps[i++].AngleDoom));
+					t.Rotate(angle.GetResult(thingprops[i++].AngleDoom));
 			}
 
 			General.Map.IsChanged = true;
 			if(OnValuesChanged != null) OnValuesChanged(this, EventArgs.Empty);
 		}
 
-		private void UpdatePitch() 
+		private void ApplyPitchChange() 
 		{
-			if (preventchanges) return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			//restore values
 			if (string.IsNullOrEmpty(pitch.Text)) 
 			{
-				foreach (Thing t in things) t.SetPitch(thingProps[i++].Pitch);
+				foreach (Thing t in things) t.SetPitch(thingprops[i++].Pitch);
 			} 
 			else //update values
 			{ 
 				foreach (Thing t in things)
-					t.SetPitch(pitch.GetResult(thingProps[i++].Pitch));
+					t.SetPitch(pitch.GetResult(thingprops[i++].Pitch));
 			}
 
 			General.Map.IsChanged = true;
-			if (OnValuesChanged != null) OnValuesChanged(this, EventArgs.Empty);
+			if(OnValuesChanged != null) OnValuesChanged(this, EventArgs.Empty);
 		}
 
 		//mxd
-		private void UpdateRoll() 
+		private void ApplyRollChange() 
 		{
-			if (preventchanges) return;
+			if(preventchanges) return;
+			MakeUndo(); //mxd
 			int i = 0;
 
 			//restore values
 			if (string.IsNullOrEmpty(roll.Text)) 
 			{
-				foreach (Thing t in things) t.SetRoll(thingProps[i++].Roll);
+				foreach (Thing t in things) t.SetRoll(thingprops[i++].Roll);
 			} 
 			else //update values
 			{ 
 				foreach (Thing t in things)
-					t.SetRoll(roll.GetResult(thingProps[i++].Roll));
+					t.SetRoll(roll.GetResult(thingprops[i++].Roll));
 			}
 
 			General.Map.IsChanged = true;
diff --git a/Source/Core/Windows/VertexEditForm.cs b/Source/Core/Windows/VertexEditForm.cs
index 076ecdfc..7a2cf6e3 100644
--- a/Source/Core/Windows/VertexEditForm.cs
+++ b/Source/Core/Windows/VertexEditForm.cs
@@ -44,8 +44,9 @@ namespace CodeImp.DoomBuilder.Windows
 		#region ================== Variables
 
 		private ICollection<Vertex> vertices;
-		private bool blockUpdate; //mxd
-		private List<VertexProperties> vertexProps; //mxd
+		private bool preventchanges; //mxd
+		private bool undocreated; //mxd
+		private List<VertexProperties> vertexprops; //mxd
 
 		//mxd. Window setup stuff
 		private static Point location = Point.Empty;
@@ -53,10 +54,10 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private struct VertexProperties //mxd
 		{
-			public float X;
-			public float Y;
-			public float ZCeiling;
-			public float ZFloor;
+			public readonly float X;
+			public readonly float Y;
+			public readonly float ZCeiling;
+			public readonly float ZFloor;
 
 			public VertexProperties(Vertex v) 
 			{
@@ -124,17 +125,12 @@ namespace CodeImp.DoomBuilder.Windows
 		// This sets up the form to edit the given vertices
 		public void Setup(ICollection<Vertex> vertices, bool allowPositionChange)
 		{
-			blockUpdate = true; //mxd
+			preventchanges = true; //mxd
 			
 			// Keep this list
 			this.vertices = vertices;
 			if(vertices.Count > 1) this.Text = "Edit Vertices (" + vertices.Count + ")";
-			vertexProps = new List<VertexProperties>(); //mxd
-
-			//mxd. Make undo
-			string undodesc = "vertex";
-			if(vertices.Count > 1) undodesc = vertices.Count + " vertices";
-			General.Map.UndoRedo.CreateUndo("Edit " + undodesc);
+			vertexprops = new List<VertexProperties>(); //mxd
 
 			////////////////////////////////////////////////////////////////////////
 			// Set all options to the first vertex properties
@@ -167,13 +163,13 @@ namespace CodeImp.DoomBuilder.Windows
 				if(positiony.Text != v.Position.y.ToString()) positiony.Text = "";
 
 				// Custom fields
-				if(General.Map.FormatInterface.HasCustomFields) { //mxd
-					v.Fields.BeforeFieldsChange();//mxd
+				if(General.Map.FormatInterface.HasCustomFields) 
+				{
 					fieldslist.SetValues(v.Fields, false);
 				}
 
 				//mxd. Store initial properties
-				vertexProps.Add(new VertexProperties(v));
+				vertexprops.Add(new VertexProperties(v));
 			}
 
 			//mxd. Height offsets
@@ -192,7 +188,22 @@ namespace CodeImp.DoomBuilder.Windows
 				}
 			}
 
-			blockUpdate = false; //mxd
+			preventchanges = false; //mxd
+		}
+
+		//mxd
+		private void MakeUndo()
+		{
+			if(undocreated) return;
+			undocreated = true;
+
+			//mxd. Make undo
+			General.Map.UndoRedo.CreateUndo("Edit " + (vertices.Count > 1 ? vertices.Count + " vertices" : "vertex"));
+
+			if(General.Map.FormatInterface.HasCustomFields)
+			{
+				foreach(Vertex v in vertices) v.Fields.BeforeFieldsChange();
+			}
 		}
 		
 		#endregion
@@ -201,19 +212,20 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void positionx_WhenTextChanged(object sender, EventArgs e) 
 		{
-			if(blockUpdate) return;
+			if(preventchanges) return;
+			MakeUndo();
 			int i = 0;
 
 			//restore values
 			if(string.IsNullOrEmpty(positionx.Text)) 
 			{
 				// Apply position
-				foreach(Vertex v in vertices) v.Move(new Vector2D(vertexProps[i++].X, v.Position.y));
+				foreach(Vertex v in vertices) v.Move(new Vector2D(vertexprops[i++].X, v.Position.y));
 			} 
 			else //update values
 			{ 
 				// Verify the coordinates
-				float px = positionx.GetResultFloat(vertexProps[i].X);
+				float px = positionx.GetResultFloat(vertexprops[i].X);
 				if(px < General.Map.FormatInterface.MinCoordinate) 
 				{
 					positionx.Text = General.Map.FormatInterface.MinCoordinate.ToString();
@@ -236,19 +248,20 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void positiony_WhenTextChanged(object sender, EventArgs e) 
 		{
-			if(blockUpdate) return;
+			if(preventchanges) return;
+			MakeUndo();
 			int i = 0;
 
 			//restore values
 			if(string.IsNullOrEmpty(positiony.Text)) 
 			{
 				// Apply position
-				foreach(Vertex v in vertices) v.Move(new Vector2D(v.Position.x, vertexProps[i++].Y));
+				foreach(Vertex v in vertices) v.Move(new Vector2D(v.Position.x, vertexprops[i++].Y));
 			} 
 			else //update values
 			{ 
 				// Verify the coordinates
-				float py = positiony.GetResultFloat(vertexProps[i].Y);
+				float py = positiony.GetResultFloat(vertexprops[i].Y);
 				if(py < General.Map.FormatInterface.MinCoordinate) 
 				{
 					positiony.Text = General.Map.FormatInterface.MinCoordinate.ToString();
@@ -271,13 +284,14 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void zceiling_WhenTextChanged(object sender, EventArgs e) 
 		{
-			if(blockUpdate) return;
+			if(preventchanges) return;
+			MakeUndo();
 			int i = 0;
 
 			//restore values
 			if(string.IsNullOrEmpty(zceiling.Text)) 
 			{
-				foreach(Vertex v in vertices) v.ZCeiling = vertexProps[i++].ZCeiling;
+				foreach(Vertex v in vertices) v.ZCeiling = vertexprops[i++].ZCeiling;
 
 			} 
 			else if(zceiling.Text == CLEAR_VALUE) //clear values
@@ -288,7 +302,7 @@ namespace CodeImp.DoomBuilder.Windows
 			else //update values
 			{ 
 				foreach(Vertex v in vertices)
-					v.ZCeiling = zceiling.GetResultFloat(vertexProps[i++].ZCeiling);
+					v.ZCeiling = zceiling.GetResultFloat(vertexprops[i++].ZCeiling);
 			}
 
 			General.Map.IsChanged = true;
@@ -297,14 +311,15 @@ namespace CodeImp.DoomBuilder.Windows
 
 		private void zfloor_WhenTextChanged(object sender, EventArgs e) 
 		{
-			if(blockUpdate) return;
+			if(preventchanges) return;
+			MakeUndo();
 			int i = 0;
 
 			//restore values
 			if(string.IsNullOrEmpty(zfloor.Text)) 
 			{
 				foreach(Vertex v in vertices)
-					v.ZFloor = vertexProps[i++].ZFloor;
+					v.ZFloor = vertexprops[i++].ZFloor;
 			
 			} 
 			else if(zfloor.Text == CLEAR_VALUE) //clear values
@@ -314,7 +329,7 @@ namespace CodeImp.DoomBuilder.Windows
 			else //update values
 			{ 
 				foreach(Vertex v in vertices)
-					v.ZFloor = zfloor.GetResultFloat(vertexProps[i++].ZFloor);
+					v.ZFloor = zfloor.GetResultFloat(vertexprops[i++].ZFloor);
 			}
 
 			General.Map.IsChanged = true;
@@ -340,7 +355,10 @@ namespace CodeImp.DoomBuilder.Windows
 		// OK clicked
 		private void apply_Click(object sender, EventArgs e)
 		{
-			//apply custom fields
+			//mxd. Make undo if required
+			MakeUndo();
+			
+			// Apply custom fields
 			if(General.Map.FormatInterface.HasCustomFields) 
 			{
 				foreach(Vertex v in vertices) fieldslist.Apply(v.Fields); //mxd
@@ -357,8 +375,8 @@ namespace CodeImp.DoomBuilder.Windows
 		// Cancel clicked
 		private void cancel_Click(object sender, EventArgs e)
 		{
-			//mxd. perform undo
-			General.Map.UndoRedo.WithdrawUndo();
+			//mxd. Perform undo if required
+			if(undocreated) General.Map.UndoRedo.WithdrawUndo();
 			
 			// And close
 			this.DialogResult = DialogResult.Cancel;