Having a problem with mouse buttons in Mame. Any ideas?

[Cue-Ball]

My cabinet was working fine until a few weeks ago.  I keep making small changes to get other emus to work and always seem to screw up something.  Right now i'm having a problem with getting my mouse buttons to work in MAME and i've tried everything i can think of to solve it but nothing seems to work.  Here's the deal:

I've got two player positions with one joystick and six buttons each.  I have another 4-way joystick that's wired in parallel to the player one stick and two buttons next to it that are wired as "mouse buttons" via the Opti-Pac.  Other than the two "mouse buttons" and my trackball, all joysticks and buttons are running through an I-Pac.  I have Mame setup to use P1B1 as either button 1 (via the I-Pac) or mouse button 0 (the first mouse button on the Opti-Pac).  I have P1B2 setup to use either button 2 (via the I-Pac) or mouse button 1 (2nd mouse button on the Opti-Pac).  This way, you can play games using either the six button layout on the left side of the CP or a two button layout in the middle of the CP (better for games like Galaga).

If i use the player 1 joystick and buttons, games all work fine.  However; if i use the "mouse buttons" for button 1 or button 2, they only work about 1 press out of every 10.  For instance, if i press button 1 that's wired through the I-Pac, i can shoot 10 shots in 1942 in a second or two.  If i try doing that with the first mouse button i can only shoot about once every few seconds.  The strange part is, the mouse buttons work perfectly in windows.  I can click and double-click very quickly.  They just don't work properly in Mame and i can't figure out why!

I already know that the buttons work, because they work fine in Windows.  So, there's obviously nothing wrong with the button, microswitch, or I-Pac.  It HAS to be a software setting somewhere.  I've tried deleting the Mame configs and making new ones but that didn't work either.  Other than the Mame config files and Windows settings, what else could possibly affect these buttons???