The ActiveWindowChanging/ActiveWindowChanged events are fired after the Drag/Drop operation is completed.
If you continue to have a issues, please give us a more detailed description of your scenario or a sample application that demonstrates the issue. Please note that you should open a new support ticket in order to be able to attach your files.
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.