When OSC 1 and 2 are tuned exactly together and a low note is played, I hear what I would describe as "inter-modulation." It sounds like some kind of random, subtle S/H filter modulation.
Set the CS-80V like so:
All filters, RM, and LFO modulation off.
All VCO, VCF, and TOUCH RESPONSE sliders off.
All VCA sliders off except "VCF LEVEL," "SUSTAIN," and "LEVEL." Set these three to maximum.
Both octave ranges = 16' [-1 octave]
MIX I/II = 0
DETUNE CH II = 0 (or as close as possible)
Square wave for both lines = ON, all other waveforms off
Now play the lowest C and hold it for several seconds. You should hear the sound jumping around within the tone. You can hear a short recording of it here
in the "CS-80V test" folder. The mp3 is called TAE_oddity.
The behavior also occurs using Sawtooth instead of Square wave, but it seems more pronounced with Square. If you don't hear the problem at first, keep holding the note for 15 seconds or so. Also, the lower the pitch the easier it is to hear.
I am using version 1.2 and it does the same thing in Mac OS 9 and OS X. I have a CS-80V 1.0 demo version on a PC at work and I did not hear the problem on that version/platform. It was totally smooth.
Hope this helps.