Thank you for writing.
Indeed, I can confirm that the event is not fired in bound mode. I have added this case in our Public Issue Tracking System
and we will address it accordingly. Feel free to add your vote for this case here: http://www.telerik.com/support/pits.aspx#/public/winforms/13315
Your Telerik Points
have been updated for this report.
Meanwhile, please use the DragEnding event instead.
I hope this helps.
All the best,
the Telerik team