The problem is that your trackball is not your MOUSE DEVICE 0. I assume you also have a mouse hooked up? My cabinet is the same way. My MOUSE is device 0 and my spinner is device 1. I had to go in to the MAME config menu (TAB) and configure my "PADDLE" and my "DIAL" as device 1 (instead of 0).
Make sure you modify MAME.INI to read "MOUSE 1".
I am probably a bit out of date with stuff...so is my trackball_device etc advice wrong? I think it is correct, but you then just have to be careful of any mouse-device-specific input mappings.
Minnie: Any news for us MAMEWAHerz soon?
Not a lot...except my todo list has got a hell of a lot bigger since checking the boards today!

That'll teach me to have some time off....