For the last decade and a few more years, I've been emulating GBA with Shift as the A button, which was never an issue.
Recently, however, when I use shift, it started causing trouble, the emulator starts behaving like any key pressed together with shift is perma-pressed (as in: if I jump while holding left, character will be stuck walking left from then on).
This doesn't happen on any other emulator of any other system (I use Shift as X on playstation, etc).
I've checked if it has anything to do with Sticky keys, but it's not.