diff --git a/src/AddIns/DisplayBindings/AvalonEdit.AddIn/Src/AvalonEditViewContent.cs b/src/AddIns/DisplayBindings/AvalonEdit.AddIn/Src/AvalonEditViewContent.cs
index d33469e276..343f8567ff 100644
--- a/src/AddIns/DisplayBindings/AvalonEdit.AddIn/Src/AvalonEditViewContent.cs
+++ b/src/AddIns/DisplayBindings/AvalonEdit.AddIn/Src/AvalonEditViewContent.cs
@@ -44,23 +44,36 @@ namespace ICSharpCode.AvalonEdit.AddIn
 			this.Files.Add(file);
 			file.ForceInitializeView(this);
 			
-			codeEditor.Document.Changed += textEditor_Document_Changed;
+			file.IsDirtyChanged += PrimaryFile_IsDirtyChanged;
+			codeEditor.Document.UndoStack.PropertyChanged += codeEditor_Document_UndoStack_PropertyChanged;
 			codeEditor.CaretPositionChanged += CaretChanged;
 			codeEditor.TextCopied += codeEditor_TextCopied;
 		}
 		
-		void codeEditor_TextCopied(object sender, ICSharpCode.AvalonEdit.Editing.TextEventArgs e)
+		void codeEditor_Document_UndoStack_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
 		{
-			TextEditorSideBar.Instance.PutInClipboardRing(e.Text);
+			PrimaryFile.IsDirty = !codeEditor.Document.UndoStack.IsOriginalFile;
 		}
 		
-		void textEditor_Document_Changed(object sender, DocumentChangeEventArgs e)
+		void PrimaryFile_IsDirtyChanged(object sender, EventArgs e)
 		{
-			if (!isLoading) {
-				PrimaryFile.IsDirty = true;
+			var document = codeEditor.Document;
+			if (document != null) {
+				var undoStack = document.UndoStack;
+				if (this.PrimaryFile.IsDirty) {
+					if (undoStack.IsOriginalFile)
+						undoStack.DiscardOriginalFileMarker();
+				} else {
+					undoStack.MarkAsOriginalFile();
+				}
 			}
 		}
 		
+		void codeEditor_TextCopied(object sender, ICSharpCode.AvalonEdit.Editing.TextEventArgs e)
+		{
+			TextEditorSideBar.Instance.PutInClipboardRing(e.Text);
+		}
+		
 		public CodeEditor CodeEditor {
 			get { return codeEditor; }
 		}
@@ -221,6 +234,7 @@ namespace ICSharpCode.AvalonEdit.AddIn
 		
 		public override void Dispose()
 		{
+			this.PrimaryFile.IsDirtyChanged -= PrimaryFile_IsDirtyChanged;
 			base.Dispose();
 			BookmarksDetach();
 			codeEditor.Dispose();
diff --git a/src/AddIns/DisplayBindings/AvalonEdit.AddIn/Src/CodeEditor.cs b/src/AddIns/DisplayBindings/AvalonEdit.AddIn/Src/CodeEditor.cs
index 2120ea0111..81b3bc977b 100644
--- a/src/AddIns/DisplayBindings/AvalonEdit.AddIn/Src/CodeEditor.cs
+++ b/src/AddIns/DisplayBindings/AvalonEdit.AddIn/Src/CodeEditor.cs
@@ -285,6 +285,7 @@ namespace ICSharpCode.AvalonEdit.AddIn
 					this.Encoding = reader.CurrentEncoding;
 				}
 			}
+			primaryTextEditor.IsModified = false;
 			NewLineConsistencyCheck.StartConsistencyCheck(this);
 		}
 		
diff --git a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/UndoStack.cs b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/UndoStack.cs
index 8e33449270..5386a4776b 100644
--- a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/UndoStack.cs
+++ b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Document/UndoStack.cs
@@ -49,11 +49,22 @@ namespace ICSharpCode.AvalonEdit.Document
 		/// </summary>
 		int elementsOnUndoUntilOriginalFile;
 		
+		bool isOriginalFile = true;
+		
 		/// <summary>
 		/// Gets whether the document is currently in its original state (no modifications).
 		/// </summary>
 		public bool IsOriginalFile {
-			get { return elementsOnUndoUntilOriginalFile == 0; }
+			get { return isOriginalFile; }
+		}
+		
+		void RecalcIsOriginalFile()
+		{
+			bool newIsOriginalFile = (elementsOnUndoUntilOriginalFile == 0);
+			if (newIsOriginalFile != isOriginalFile) {
+				isOriginalFile = newIsOriginalFile;
+				NotifyPropertyChanged("IsOriginalFile");
+			}
 		}
 		
 		/// <summary>
@@ -61,10 +72,8 @@ namespace ICSharpCode.AvalonEdit.Document
 		/// </summary>
 		public void MarkAsOriginalFile()
 		{
-			bool oldIsOriginalFile = IsOriginalFile;
 			elementsOnUndoUntilOriginalFile = 0;
-			if (!oldIsOriginalFile)
-				NotifyPropertyChanged("IsOriginalFile");
+			RecalcIsOriginalFile();
 		}
 		
 		/// <summary>
@@ -72,24 +81,20 @@ namespace ICSharpCode.AvalonEdit.Document
 		/// </summary>
 		public void DiscardOriginalFileMarker()
 		{
-			bool oldIsOriginalFile = IsOriginalFile;
 			elementsOnUndoUntilOriginalFile = int.MinValue;
-			if (oldIsOriginalFile)
-				NotifyPropertyChanged("IsOriginalFile");
+			RecalcIsOriginalFile();
 		}
 		
 		void FileModified(int newElementsOnUndoStack)
 		{
-			if (newElementsOnUndoStack == 0 || elementsOnUndoUntilOriginalFile == int.MinValue)
+			if (elementsOnUndoUntilOriginalFile == int.MinValue)
 				return;
 			
-			bool oldIsOriginalFile = IsOriginalFile;
 			elementsOnUndoUntilOriginalFile += newElementsOnUndoStack;
 			if (elementsOnUndoUntilOriginalFile > undostack.Count)
 				elementsOnUndoUntilOriginalFile = int.MinValue;
 			
-			if (oldIsOriginalFile != IsOriginalFile)
-				NotifyPropertyChanged("IsOriginalFile");
+			// don't call RecalcIsOriginalFile(): wait until end of undo group
 		}
 		#endregion
 		
@@ -220,11 +225,11 @@ namespace ICSharpCode.AvalonEdit.Document
 				} else if (actionCountInUndoGroup > 1) {
 					// combine all actions within the group into a single grouped action
 					undostack.PushBack(new UndoOperationGroup(undostack, actionCountInUndoGroup));
-					actionCountInUndoGroup = 1; // actions were combined
+					FileModified(-actionCountInUndoGroup + 1 + optionalActionCount);
 				}
 				EnforceSizeLimit();
 				allowContinue = true;
-				FileModified(actionCountInUndoGroup);
+				RecalcIsOriginalFile(); // can raise event
 			}
 		}
 		
@@ -261,6 +266,7 @@ namespace ICSharpCode.AvalonEdit.Document
 					state = StateListen;
 				}
 				FileModified(-1);
+				RecalcIsOriginalFile();
 				if (undostack.Count == 0)
 					NotifyPropertyChanged("CanUndo");
 				if (redostack.Count == 1)
@@ -294,6 +300,7 @@ namespace ICSharpCode.AvalonEdit.Document
 					state = StateListen;
 				}
 				FileModified(1);
+				RecalcIsOriginalFile();
 				if (redostack.Count == 0)
 					NotifyPropertyChanged("CanRedo");
 				if (undostack.Count == 1)
@@ -347,6 +354,8 @@ namespace ICSharpCode.AvalonEdit.Document
 				actionCountInUndoGroup++;
 				if (isOptional)
 					optionalActionCount++;
+				else
+					FileModified(1);
 				EndUndoGroup();
 				if (wasEmpty)
 					NotifyPropertyChanged("CanUndo");
diff --git a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/TextEditor.cs b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/TextEditor.cs
index 4cf4930419..e4fbbdd2b1 100644
--- a/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/TextEditor.cs
+++ b/src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/TextEditor.cs
@@ -406,7 +406,7 @@ namespace ICSharpCode.AvalonEdit
 		/// </summary>
 		public bool IsModified {
 			get { return (bool)GetValue(IsModifiedProperty); }
-			set { SetValue(IsModifiedProperty, value); }
+			set { SetValue(IsModifiedProperty, Boxes.Box(value)); }
 		}
 		
 		static void OnIsModifiedChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)