One thing I noticed was the Shift key triggering the Sticky Keys warning on Windows after pressing it several times. You might want to assign a different key for that. (Happened to me, maybe check if others experience it too!)
But there are few other combinations I added just in case, you could try use Z+X or N+M buttons for jump+dig. Also game might work with gamepad, which support I did try add, but didn't try out.
