this is weird, it seems like the "Mod Depth" knob becomes "stepped" when you set the LFO to square.
to test this yourself, assign LFO to oscillator pitch, set the LFO to square wave, lower the LFO speed down to slowest it can go, wait for it to go to the "upper part" of the square wave, the higher pitch, and turn the "Mod Depth" knob as slowly as you can. you'll hear the LFO Depth knob audibly step.
if you set the Mod Depth knob at the precise point between two "steps", the LFO tuning becomes unstable.
I tried this with the LFO set to triangle wave, but nothing weird, behaves normally, no stepping felt on the mod depth knob while the LFO is going on triangle. it only happens when it's set to square.
where the "stepping" happens seems to depend on the temperature of the synth. as the synth warms up, the positions where the "steps" are will change. this may not be a big deal, but say you're trying to set the square LFO to be a perfect octave. if the synth is a certain temp and the mod depth knob "step" lies right upon the octave, you'll get unstable tuning. this is actually how I first accidentally discovered this behavior.
edit: video
https://drive.google.com/open?id=1DBq1J94agyJatrqjhLJnxkpZbX0AXFhW
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