Hi Micheal,
Thank you for the update.
If you need the Selection changing after the drag operation in GridControl. You have handled the MouseDown event to perform the Drag operation in GridControl, so please try using conditional variables in MouseDown and MouseUp event to achieve this behavior.
We have created the sample to change the selection in GridControl, refer the sample in below link:
http://files.syncfusion.com/support/samples/Grid.Windows/Forums/VirtualSelection.zipThis sample demonstrate manually to select the Row in GridControl, when the Drag action has been performed in Selected row.
Let me know if you have any queries.
Regards,
Lingaraj S.