Also there don't appear to be any posts reporting this since CS6, which makes it a bit strange that I get it happening on two unrelated installs.
So, being at a loss, does anyone else have any idea why this might be happening?
Well, straight up: You are operating on generalized assumptions without providing any useful technical info. You cannot find any reports because you are operating with vagueries. That's like searching Google with a generic term like "blue sky" - millions of hits, but not a single one must necessarily meet your criteria. Each and every of the separate instances could have completely different causes and well, from a technical point of view, you would have to describe exactly what you did every time before anyone can even begin to decipher what could be going on.
Mylenium