Loadman,
Okay, experiments are complete.
1) It's definitely not the USB 2.0 PCI Host Controller. I cannot scroll on startup with the Minipac and spinners plugged into the Controller or the mobo.
2) Tried my last setup, Mala 1.6.6.3 Beta. NO PROBLEMS. I can scroll on startup. This was true for both the USB Controller and the mobo.
Another observation: I spent yesterday creating a new MAME list within Mala 1.735 (right click, add this game to [other] list). In 1.73, when I would leave the sub-window, my mouse cursor would be visible (and I am unable to scroll), until I left click. In 1.6.6.3, same behavior, BUT the mouse cursor is not visible.