It is a bug and we will fix it. Actually it was reported ago, but we missed to fix it for some reason. Thank you for remind us now.
Meanwhile to our next release you can make some small changes in the source code of the controls to make it work for you. Check this forum thread for more information:
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!