I had noticed this a while ago working on CCEmuX, but hadn't been able to reproduce it in CC. I noticed today that it only happens on monitors - not computers, turtles, or pocket computers. A picture is worth a thousand words, so here's a short video of the issue.

I've quickly skimmed over the source for worm, but haven't seen anything obvious yet.

That'd be this line here, presumably used for debugging purposes and then never disabled.