As far as i can tell, then the OSC Sync function in CS-80 is not working like it should.
Arturia please check this function, changing the synced OSC 2 pitch in different ways. Also using the modulation matrix to make larger detunings.
Beside there seem to be a bad sound, then when the OSCs are synced and tuned equal there should be no phaseshift relationship behavior at all, even if both OSCs sound is heard. And when changing the pitch of OSC2 the overall pitch as such should not change, but just create the the phaseshift relationship complex waveform. But the main pitch do change.
This is from the manual:
"The synchronization of an oscillator with another creates more complex waveforms. If for example, you synchronize oscillator2 with oscillator1, oscillator2 will restart a new period every time the first oscillator completes a period, even if oscillator2 has not completed a complete period (this signifies that it is not tuned to the same tonality.) The more you tune oscillator2 upwards, the more you will encounter composite waveforms."