It is hard for me to guess what could cause this. Could you please provide us with a code snippets that we might use to create a runnable solution? This way we'll be able to investigate the unwanted behavior locally and get back to you with our feedback based on the code.
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