diff --git a/Source/Core/Editing/UndoManager.cs b/Source/Core/Editing/UndoManager.cs
index a6acad1..1549408 100644
--- a/Source/Core/Editing/UndoManager.cs
+++ b/Source/Core/Editing/UndoManager.cs
@@ -718,24 +718,19 @@ namespace CodeImp.DoomBuilder.Editing
 							//General.MainWindow.RedrawDisplay();
 
 							// (Re)set hacky flat alignment
-							bool alignmentupdate = false;
 							foreach (Linedef l in General.Map.Map.Linedefs)
 								if (l.Marked && (l.IsFlatAlignment || l.Action == 0))
 								{
 									l.Front.Sector.UpdateFloorSurface();
 									l.Front.Sector.UpdateCeilingSurface();
 									linedeftags.Add(l.Tag);
-									alignmentupdate = true;
 								}
-							if (alignmentupdate)
-							{
-								foreach (Sector s in General.Map.Map.Sectors)
-									if (linedeftags.Contains(s.Tag))
-									{
-										s.UpdateFloorSurface();
-										s.UpdateCeilingSurface();
-									}
-							}
+							foreach (Sector s in General.Map.Map.Sectors)
+								if (linedeftags.Contains(s.Tag) || s.Marked)
+								{
+									s.UpdateFloorSurface();
+									s.UpdateCeilingSurface();
+								}
 
 							// Map changed!
 							General.Map.IsChanged = true;
@@ -882,24 +877,19 @@ namespace CodeImp.DoomBuilder.Editing
 							//General.MainWindow.RedrawDisplay();
 
 							// (Re)set hacky flat alignment
-							bool alignmentupdate = false;
 							foreach (Linedef l in General.Map.Map.Linedefs)
 								if (l.Marked && (l.IsFlatAlignment || l.Action == 0))
 								{
 									l.Front.Sector.UpdateFloorSurface();
 									l.Front.Sector.UpdateCeilingSurface();
 									linedeftags.Add(l.Tag);
-									alignmentupdate = true;
 								}
-							if (alignmentupdate)
-							{
-								foreach (Sector s in General.Map.Map.Sectors)
-									if (linedeftags.Contains(s.Tag))
-									{
-										s.UpdateFloorSurface();
-										s.UpdateCeilingSurface();
-									}
-							}
+							foreach (Sector s in General.Map.Map.Sectors)
+								if (linedeftags.Contains(s.Tag) || s.Marked)
+								{
+									s.UpdateFloorSurface();
+									s.UpdateCeilingSurface();
+								}
 
 							// Map changed!
 							General.Map.IsChanged = true;
diff --git a/Source/Core/Windows/SectorEditForm.cs b/Source/Core/Windows/SectorEditForm.cs
index c7049e0..4743159 100644
--- a/Source/Core/Windows/SectorEditForm.cs
+++ b/Source/Core/Windows/SectorEditForm.cs
@@ -324,6 +324,10 @@ namespace CodeImp.DoomBuilder.Windows
 
 				// Action
 				s.Tag = General.Clamp(tagSelector.GetSmartTag(s.Tag, tagoffset++), General.Map.FormatInterface.MinTag, General.Map.FormatInterface.MaxTag); //mxd
+
+				// Update hacky flat alignment
+				s.UpdateFloorSurface();
+				s.UpdateCeilingSurface();
 			}
 
 			// Done
diff --git a/Source/Plugins/BuilderModes/ClassicModes/DragGeometryMode.cs b/Source/Plugins/BuilderModes/ClassicModes/DragGeometryMode.cs
index 0e37ec2..923cd99 100644
--- a/Source/Plugins/BuilderModes/ClassicModes/DragGeometryMode.cs
+++ b/Source/Plugins/BuilderModes/ClassicModes/DragGeometryMode.cs
@@ -517,6 +517,30 @@ namespace CodeImp.DoomBuilder.BuilderModes
 						}
 					}
 				}
+				else 
+				{
+					// Update hacky flat alignment
+					foreach (Linedef l in General.Map.Map.LinedefsFromMarkedVertices(true, true, true))
+					{
+						if (l.IsFlatAlignment)
+						{
+							if (l.Tag == 0)
+							{
+								l.Front.Sector.UpdateFloorSurface();
+								l.Front.Sector.UpdateCeilingSurface();
+							}
+							else
+							{
+								foreach (Sector s in General.Map.Map.Sectors)
+									if (s.Tag == l.Tag)
+									{
+										s.UpdateFloorSurface();
+										s.UpdateCeilingSurface();
+									}
+							}
+						}
+					}
+				}
 				
 				// Update cached values
 				General.Map.Map.Update();