you CAN have some issues depending on the keys the IPAC4 is mapped to at times. Some of the old mame games may not recognize a few of the goofier keys setup as the inputs on the IPAC4, especially on player 3 and player 4 where you start to run out of keys and get a but wackier.
I have had issues with that. Then, I have had issues where you dont realize the damn thing has duplicates between certain buttons between players. Up is V for XYZ player but "V" is also assigned to another input on the ipac on another player.
Lastly, the thing I would check is Retroarch itself. IF you check the two above and confirm thats all good, the last issue I have had with IPAC4 versus Retroarch is that retroarch will not assign the specific key correctly. I have had the "UP" key assign through the UI as "Keypad8" from the numpad. I had to get around this by manually changing them in the CFG file itself. Then everything worked.
Extra lastly, I am assuming you only playing older style games and keeping the IPAC4 in keyboard input mode. IF you are changing the mode to controllers, all bets are off.
