Thank you for writing.
This is a known issue. However, at the moment we are not aware of the reason for it. We have already added this issue to our issue tracking system and it will be addressed in one of our future releases.
the Telerik team
Q3’10 SP1 of RadControls for WinForms is available for download
; also available is the Q1'11 Roadmap
for Telerik Windows Forms controls.