I finally have my cabinet control panel wired, and started doing some 'testing' 
I have a trackball, spinner, and two push buttons wired to the Opti-PAC and several other sticks and buttons wired to an I-PAC -- both in USB mode. The I-PAC seems to work fine, but I'm seeing really strange behavior with the two buttons I have wired to the OptiPAC as mouse buttons. Sometimes the button activates a double-click when I press it once (like if I single click on a file in explorer, it will launch it as if I double clicked). Sometimes it doesn't register when I press and hold the button (making dragging and dropping impossible). I've checked the connections and they seem to be fine. Has anyone seen anything like this before? The two buttons are only connected to the Opti-PAC (i.e. they are not also connected to the IPAC).
Thx,
Andy
Make sure the buttons are on the same player # as the device you want to use to drag and drop. IE, if the trackball is wired to optipac's "trackball, player 2" inputs, wire the buttons also to player 2.
Also, any movements sent to the computer from different USB mouse devices than the one with buttons can make windows think the button isn't pressed when it is. Since the optipac in USB mode is two USB mice (one player 1, the other player 2), having the sppinner and trackball on the same player (tball P1 & rotary P1, for example) will let optipac prevent any confusion the computer might get if both moved at the same. However, if you have another mouse device installed, make sure it isn't moving also. I have problems if I use a trackball, and my USB optical mouse is plugged in but not sitting on a flat surface; it sends small "tick" movements that screws up the button signals from the trackball.