Quick addition: I think there's also something wrong with the X-arcade. Even on my main PC it does seem to stick, only that I notice it a lot less in MAME, in fact I just played an hour without it happening. However in final burn or neo rage it's pretty apparent and happens all the time.
I was thinking just to get an I-Pac and take out the X-Arcade PCB. Surely that would cure the problem.
You know it makes sense!