I got it... or, at least I understand what is happening.

When I leave the row while still in the cell, the cell is still dirty and has not updated. If on a new row (which I always was), the cell value starts as null. It seems to call dtaContacts_RowLeave() before changing the dirty state. Now I just need to force change the dirty state before calling RowLeave(). Thank you everyone for your assistance!