The problem is that we are using a Transparent window to host the floating panes and the WinForms Host doesn't support to be placed inside a transparent window. We are currently working on the RadDocking control and we are targeting this problem, but the fix will not be ready for Q1 2011.
All the best,
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!