OK, I was able to disconnect my old Dell clicky PS/2 keyboard from my OmniCube KVM, from Y2K, to connect directly to my desktop PC to retest. I easily reproduce it. So, it's not a KVM issue.
I am starting to notice a pattern. If I start up TI 99/4A, keys work fine until I quit that session and relaunch it/another cartridge. The key input stops working correctly until I exit MAME fully and retry. It seems like key inputs aren't reinitalized correctly between booted up session? I also did notice a few times, MAME would freeze and crash (goes away) after a few seconds without any error messages.
Last edited by antdude; 08/13/16 07:59 PM.