Casio CZ/ VZ/ FZ - Pro Series

Hi all,

I have recently been using my CZ-101 with a Roland MC-500 sequencer, taking advantage of the 4 voice multitimbrality.  However, when I assign the voices using the MIDI parameter (where the first voice is 'n,' the next is 'n + 1' and so on), the often randomly change on me.  I have found that sometimes I can rectify this by manually setting the voices I want on each separate MIDI channel, THEN going back and doing assigning all 4 voices on the on 'n' channel, but this doesn't always work.  Is there something really obvious that I am missing here?  It is kind of a bummer when some twinkly chimes drop in lieu of a fat bassline.  ;)

Thanks in advance!