I have not used MTB much, but have dabbled with in in the past. Those Csys showed for me too on NX12 and way back to NX10.
I just ignored them, since I do not use it daily. Just letting you know its not just you, and not just NX12. There were times I would even see a line of 100's of them in a row after moving a component around. I would restart the session, and they would disappear. "Refresh" and "Regenerate Work" didn't do anything either.