I faced problems with the text selection while using the RadRichTextBox. These problems occurred as soon as I updated to version 2013.3.1204. In older versions I could not reproduce this behavior.
You can reproduce this behavior in the telerik examples on your website (e.g. RichTextBox Customize Presentation demo).
a. Select the whole document (Ctrl+A)
a capital letter
c. => The selection is completely broken and behaves very strangely. In my application this leads to a frozen RadRichTextBox.
a. Select a certain text
b. Type a capital letter
c. => The remaining line is selected.