Casio CZ/ VZ/ FZ - Pro Series

Any idea what's causing my CZ to randomly re-set itself??

It turns on fine, and plays fine, but every now and then, it will 
reset itself, and go back to internal patch A1 (Brass Ens). Also, the 
Tone Mix, Key Split, Normal and MIDI buttons are always lit, but can 
still be used. 
Very strange I know, my first thought would be a power supply issue, 
but the button thing makes me wonder. Of course it could be unrelated, 
but I'd like to see if anyone else has any ideas.