diff --git a/Source/Editing/UndoManager.cs b/Source/Editing/UndoManager.cs
index 1907063c..355fbd45 100644
--- a/Source/Editing/UndoManager.cs
+++ b/Source/Editing/UndoManager.cs
@@ -87,7 +87,7 @@ namespace CodeImp.DoomBuilder.Editing
 
 			// Start background thread
 			backgroundthread = new Thread(new ThreadStart(BackgroundThread));
-			backgroundthread.Name = "Background Loader";
+			backgroundthread.Name = "Snapshot Compressor";
 			backgroundthread.Priority = ThreadPriority.Lowest;
 			backgroundthread.IsBackground = true;
 			backgroundthread.Start();
@@ -374,16 +374,10 @@ namespace CodeImp.DoomBuilder.Editing
 							// Reset grouping
 							lastgroup = UndoGroup.None;
 
-							lock(u)
-							{
-								// Change map set
-								if(u.IsOnDisk)
-								{
-									u.StoreOnDisk = false;
-									u.RestoreFromFile();
-								}
-								General.Map.ChangeMapSet(new MapSet(u.MapData));
-							}
+							// Change map set
+							MemoryStream data = u.GetMapData();
+							General.Map.ChangeMapSet(new MapSet(data));
+							data.Dispose();
 							
 							// Remove selection
 							General.Map.Map.ClearAllMarks(false);
@@ -407,7 +401,7 @@ namespace CodeImp.DoomBuilder.Editing
 		
 		// This performs a redo
 		[BeginAction("redo")]
-		internal void PerformRedo()
+		public void PerformRedo()
 		{
 			UndoSnapshot u, r;
 			Cursor oldcursor = Cursor.Current;
@@ -455,16 +449,10 @@ namespace CodeImp.DoomBuilder.Editing
 						// Reset grouping
 						lastgroup = UndoGroup.None;
 
-						lock(r)
-						{
-							// Change map set
-							if(r.IsOnDisk)
-							{
-								r.StoreOnDisk = false;
-								r.RestoreFromFile();
-							}
-							General.Map.ChangeMapSet(new MapSet(r.MapData));
-						}
+						// Change map set
+						MemoryStream data = r.GetMapData();
+						General.Map.ChangeMapSet(new MapSet(data));
+						data.Dispose();
 						
 						// Remove selection
 						General.Map.Map.ClearAllMarks(false);
diff --git a/Source/Editing/UndoSnapshot.cs b/Source/Editing/UndoSnapshot.cs
index 346ddf0d..a39c7a3b 100644
--- a/Source/Editing/UndoSnapshot.cs
+++ b/Source/Editing/UndoSnapshot.cs
@@ -52,10 +52,9 @@ namespace CodeImp.DoomBuilder.Editing
 
 		#region ================== Properties
 
-		internal MemoryStream MapData { get { return mapdata; } }
 		public string Description { get { return description; } }
 		public int TicketID { get { return ticketid; } }
-		public bool StoreOnDisk { get { return storeondisk; } set { storeondisk = value; } }
+		internal bool StoreOnDisk { get { return storeondisk; } set { storeondisk = value; } }
 		public bool IsOnDisk { get { return isondisk; } }
 		
 		#endregion
@@ -83,7 +82,7 @@ namespace CodeImp.DoomBuilder.Editing
 		}
 
 		// Disposer
-		public void Dispose()
+		internal void Dispose()
 		{
 			lock(this)
 			{
@@ -99,8 +98,21 @@ namespace CodeImp.DoomBuilder.Editing
 		
 		#region ================== Methods
 
+		// This returns the map data
+		internal MemoryStream GetMapData()
+		{
+			lock(this)
+			{
+				// Restore into memory if needed
+				if(isondisk) RestoreFromFile();
+				
+				// Return a copy of the buffer
+				return new MemoryStream(mapdata.ToArray());
+			}
+		}
+		
 		// This moves the snapshot from memory to harddisk
-		public void WriteToFile()
+		internal void WriteToFile()
 		{
 			lock(this)
 			{
@@ -117,7 +129,7 @@ namespace CodeImp.DoomBuilder.Editing
 				filename = General.MakeTempFilename(General.Map.TempPath, "snapshot");
 
 				// Write data to file
-				File.WriteAllBytes(filename, outstream.GetBuffer());
+				File.WriteAllBytes(filename, outstream.ToArray());
 
 				// Remove data from memory
 				mapdata.Dispose();
@@ -127,7 +139,7 @@ namespace CodeImp.DoomBuilder.Editing
 		}
 
 		// This loads the snapshot from harddisk into memory
-		public void RestoreFromFile()
+		internal void RestoreFromFile()
 		{
 			lock(this)
 			{
@@ -142,7 +154,7 @@ namespace CodeImp.DoomBuilder.Editing
 				MemoryStream outstream = new MemoryStream((int)instream.Length * 4);
 				instream.Seek(0, SeekOrigin.Begin);
 				BZip2.Decompress(instream, outstream);
-				mapdata = new MemoryStream(outstream.GetBuffer());
+				mapdata = new MemoryStream(outstream.ToArray());
 				
 				// Clean up
 				instream.Dispose();