BigBox menu control problem with 2 IPAC2 boards

[SoloTSi97]

I have a 4-player cabinet with two IPAC2 boards running BigBox exclusively for MAME games. Each IPAC2 interface handles two sets of controls. One IPAC2 is mapped with the default P1 & P2 key mappings and the second was reconfigured to reflect P3 & P3 controls. Once in a 4p game (e.g., The Simpsons), all four control stations work as expected. I've had the 4p cabinet for a while now but it only had one IPAC2 board and only two sets of controls were hooked up. I added the second IPAC2 and connected the additional two sets of controls today.

But, if both boards are connected the BigBox menu won't work correctly. It seems as if BigBox detects something is continuously pressing "left" so my games menu is stuck scrolling through the letter index (A, B, C, etc., rather than individual games). If I unplug either IPAC2 board, the menu starts working properly (it doesn't matter which one I unplug). I can launch a game, reconnect the second board, and play as expected.

I've used Notepad and a keyboard tester web site to confirm that there IS NOT a key/button stuck. Every joystick direction and button reflects the correct keypress accurately using the keyboard tester site.

Anyone else out there using two ipac2s in a 4p cabinet? Or, any suggestions?

Thanks!

[SoloTSi97]

For what it's worth, I also emailed Ultimarc. They aren't aware of an issue running two ipac2 boards or an issue with Launchbox/Bigbox in that configuration. I'm really stumped. I don't understand why bigbox would behave like a key is stuck if other tools confirm that a key is not stuck.