There were a lot of changes for the Q2 as we made a refactoring of RadWindow that should improve performance. However we introduced some unwanted issues that we are currently working to resolve. We fixed a similar bug this week. The fix will be included in the internal build on Monday. Could you please give it a try and let us know if the problem persist.
the Telerik team
Register for the Q2 2011 What's New Webinar Week. Mark your calendar for the week starting July 18th and book your seat for a walk through of all the exciting stuff we will ship with the new release!