Discussion about the Korg PolySix synthesizer

I have a polysix which was working fine yesterday, but
today when I press the middle 'D' key, the polysix 
automatically switches to 'unison' mode. Pressing 'D'
again gives a garbled output, but all other keys work
OK. The 'D' is the d in the 3rd octave from the left. The
'd' in the 4th octave also does the same. All other keys
are fine.

I also noticed that when I switch on the polysix, it defaults
to UNISON mode and also voice 1 is sounding. This is 
true even if the keyboard is unplugged, so its not a faulty
keyboard.

Any ideas what this bizare behaviour might be. I dont have
a schematic so not able to check. 

My polysix is fitted with a new KLM-377 board which has
been working perfectly, and otherwise appears to work
fine.

Ian.