Bug: Adding a figure -> smile leads to error message that you can only close by killing an application.
more thorough description (follow these simple steps to reproduce this issue/bug) :
1) Open Telerik WPF Demos projects for RadRichTextBox.
2) Try adding a figure -> smile.
3) Enjoy watching an infinite error message that you can't ever lose. The only way out is to close the application with task manager.