I was not able to replicate the issue on my side. I prepared a small sample and attached it to this thread. Could you please give it a try and let me know how it differs from your real setup?
All the best,
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed