Is it a fairly new ipac4 and uses the latest winipac for programming? The older ipac4 requires the older winipac program and the board has a jumper to enable the use of standard mame default or programmed inputs. Remember the ipac4 will output whatever keycodes that are programmed to the chip - not necessarily what the winipac program is displaying.
I recommend opening up notepad and just pressing each button in succession. Do these relate to the mame default buttons
Arrow Keys Controller (Player 1)
Left Ctrl Fire 1 (Player 1)
Left Alt Fire 2 (Player 1)
Space Fire 3 (Player 1)
Left Shift Fire 4 (Player 1)
Z Fire 5 (Player 1)
X Fire 6(Player 1)
R,F,G,D Controller (Player 2)
A Fire 1 (Player 2)
S Fire 2 (Player 2)
Q Fire 3 (Player 2)
W Fire 4 (Player 2)