No I haven't tried it via the PS/2 port yet. My MAME PC is my desktop PC and my kb cable is not quite long enough to make it back from the cab to my desk.
However, I *think* I tried using the PS/2 Interface waaaay back when and whenever I hit a button on the CP, by PC (WinXP would reboot).
As to what exact problem I'm experienceing: SMB3 you use one button to run, one button to jump, and the joystick to control direction. At irregular, but frequent intervals, one of these funvtions won't work.
For example, I'll be running right, and the jump button doesn't work. Or, I'll be running while still having the jump button pressed, and I still can't change direction.
Thanks for the info. so far