I am sorry to say but this is an unknown issue to us. Could you please send us a sample project in which this problem replicates? Also I suggest that you examine this
help article which might prove helpful.
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