USB mouse only works if PS2 mouse plugged in
 

I swear I remember seeing a post on this problem somewhere back when I was trying to get my hack working with PS2 keyboard/mouse. I finally gave up and bought a Logitech keyboard and all was fine with iPC and iDeneb, but now I have finally gotten my vanilla install working (thanks to posters here) and suddenly my usb mouse won't work without a PS2 mouse plugged in. All is fine if I boot the iPC or iDeneb partitions, so it is something in this install. Anyone know the solution?