Joystick working in MaLa (and Windows) but not MAME?

[Galvatron]

Hi there, hopefully this is something dumb that I'm missing, but I just can't figure it out for the life of me.  This is my first MAME cab.

I've got two Ultimarc 360s plugged into a PC running TinyXP, assigned to Controller 1 and 2.  They work fine in MaLa (I'm scrolling through the game list with no issues), and they look fine in the Control Panel (Game Controllers shows them moving the crosshairs in the expected manner).

However, once I select a game and launch into MAME itself, I have all kinds of problems.  MAME won't recognize any of my directional inputs no matter what I do.  Sometimes it registers a constant directional input in some direction (so far I've had it go down constantly and to the left constantly, but sometimes it doesn't move at all).

I have tried the following troubleshooting steps:
joystick is set to 1 in mame.ini
I have tried each of the 360s independently in the Controller 1 spot, both display the same issues.
I have tried remapping as either analog or 8-way, but both modes display the same constant-directional input issue.
Again, both show as properly centered in the Control Panel and are properly responsive within the MaLa frontend.

Any ideas folks?  I'm going crazy over here... 

Edit for more info: I just tried it on my laptop, running Windows 8, and have no problems.  Could it be something to do with TinyXP?