I tried to replicate the issue which you described, but to no avail. Attached to this message, you will find the code which I used for testing. Please, take a look at it and let me know if there are any differences at your end, which I may be leaving out.
In order to further investigate the issue you could send us the aspx declaration which with all styles in order to replicate the issue at our end.
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 now.