Hi Andrew,
This is being reported on 2 or 3 places on the forums, and I still am not able to reproduce.
Please see if you can come up with a minimal sample app that can reproduce this, allthough it's sometimes and sometimes not. We need an application like.
I just tested a simple DataGridView in 6.3.10, which is currently like 6.3.9 with the PatchTheme applied, and I am not able to get this error, no matter where I click all around.
If you can create the app, then as usual clean it, and email it to support (email address in signature). Please leave a note here when you do, as well as including the full http reference to this thread so we know where it came from.
Palli