Actually, after some time spent on trying to find solution about your question, I have managed to discover one. You can create a custom MultiColumnComboBox control, which overrides ProcessCmdKey. In this event, if a tab press was detected - use ClosePopup method to close the drop down. Please consider the following code as example:
CustomMultiColumnComboBox : RadMultiColumnComboBox
Message msg, Keys keyData)
I hope this helps. Let me know if you have any additional questions.
All the best,
the Telerik team
Q1’11 SP1 of RadControls for WinForms is available for download
; also available is the Q2'11 Roadmap
for Telerik Windows Forms controls.