Good day!
 
If you run any of the following waves through the comb filter in Z3TA 2 and play with the polyphony set to more than 1, you get nasty sounds. The higher you turn the resonance, the more disturbing it becomes:
 
triangle, vintage triangle, baz it 1, baz it 2, additive 2, additive 4, additive 5, organ 1, organ 2, fret, sine^2, sine^3, very noisy, who knows, user 2, generated sine.
 
Is this a bug?

BUMP! No one?

Seems to be working normally for me.
 
An update came out recently. Maybe give that a try?

Yes, I have the latest version (2.2.3).
 
Did you try those specific wave forms I mentioned? It only happens when 2 or more notes overlap. It does not happen when polyphony is set to 1. Try play some lower to mid notes. Not higher ones.

I tried several of those waves, and I get normal behavior. 

I have attempted to recreate the problem and have failed. Maybe I don't know what to listen for. I'm sure I don't know what you're hearing.
 
Any chance you could create a quick sample .WAV and give the specific setup in Z3TA (initial patch if any, wave, and specific changes to the patch (like switching to the comb filter))? Upper register and lower register, each with minimum and maximum resonance? So, 4 samples.

I can't confirm the bug as my attempts all sound good.  TheMaartian had a good suggestion.  Give us a specific example of what you're hearing and how it comes about.