MAME - Control Issue with Air Combat 22

This only happens with AC22. Doesn't happen with the first game or any other games. For whatever reason, even though I have the controls mapped to a six-button Genesis controller (the Retrobit one) movement of the plane only works with the arrow keys. All other game functions work on the controller. It's just movement. I checked the input settings and it showed the D-pad for each direction. It's very difficult to play with one hand on the arrow keys and the other on the controller buttons.