diff --git a/ICSharpCode.AvalonEdit.Tests/Highlighting/RichTextTests.cs b/ICSharpCode.AvalonEdit.Tests/Highlighting/RichTextTests.cs
new file mode 100644
index 0000000..0935a58
--- /dev/null
+++ b/ICSharpCode.AvalonEdit.Tests/Highlighting/RichTextTests.cs
@@ -0,0 +1,43 @@
+// Copyright (c) 2014 AlphaSierraPapa for the SharpDevelop Team
+// 
+// Permission is hereby granted, free of charge, to any person obtaining a copy of this
+// software and associated documentation files (the "Software"), to deal in the Software
+// without restriction, including without limitation the rights to use, copy, modify, merge,
+// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
+// to whom the Software is furnished to do so, subject to the following conditions:
+// 
+// The above copyright notice and this permission notice shall be included in all copies or
+// substantial portions of the Software.
+// 
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
+// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
+// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+using NUnit.Framework;
+
+namespace ICSharpCode.AvalonEdit.Highlighting
+{
+	[TestFixture]
+	public class RichTextTests
+	{
+		[Test]
+		public void ConcatTest()
+		{
+			var textModel = new RichTextModel();
+			textModel.SetHighlighting(0, 5, new HighlightingColor { Name = "text1" });
+			var text1 = new RichText("text1", textModel);
+
+			var textModel2 = new RichTextModel();
+			textModel2.SetHighlighting(0, 5, new HighlightingColor { Name = "text2" });
+			var text2 = new RichText("text2", textModel2);
+
+			RichText text3 = RichText.Concat(text1, RichText.Empty, text2);
+			Assert.AreEqual(text1.GetHighlightingAt(0), text3.GetHighlightingAt(0));
+			Assert.AreNotEqual(text1.GetHighlightingAt(0), text3.GetHighlightingAt(5));
+			Assert.AreEqual(text2.GetHighlightingAt(0), text3.GetHighlightingAt(5));
+		}
+	}
+}
diff --git a/ICSharpCode.AvalonEdit/Highlighting/RichTextModel.cs b/ICSharpCode.AvalonEdit/Highlighting/RichTextModel.cs
index c4fe2b6..261de31 100644
--- a/ICSharpCode.AvalonEdit/Highlighting/RichTextModel.cs
+++ b/ICSharpCode.AvalonEdit/Highlighting/RichTextModel.cs
@@ -154,8 +154,8 @@ namespace ICSharpCode.AvalonEdit.Highlighting
 		{
 			Debug.Assert(newOffsets.Length == newColors.Length);
 			Debug.Assert(newOffsets[0] == 0);
-			// remove everything before offset:
-			while (stateChangeOffsets.Count > 0 && stateChangeOffsets.Last() <= offset) {
+			// remove everything not before offset:
+			while (stateChangeOffsets.Count > 0 && stateChangeOffsets.Last() >= offset) {
 				stateChangeOffsets.RemoveAt(stateChangeOffsets.Count - 1);
 				stateChanges.RemoveAt(stateChanges.Count - 1);
 			}