Thank you for writing.
I replicated the exception you describe. The issue is logged to our Public Issue Tracker under ID 13880. To vote for it and subscribe to its status updates follow this link: http://www.telerik.com/support/pits.aspx#/public/winforms/13880
. Please excuse us for the caused inconvenience. We will do our best to address the issue in a future release. I have updated your Telerik points for this report report.
One approach to avoid the exception is to create a custom RadTreeViewElement and override its EndEditCore method. This suggestion is implemented in the attached sample project. I hope you find it useful.
Let me know if you encounter further issues.
the Telerik team