Cyan Magenta Yellow Butts
This is the best Illustrator bug ever and I hope they never fix it.
Apparently this has been in Adobe Illustrator since at least 2014, and that app has been rewritten at least once since then, as I recall.
Quite why Adobe haven’t hired Peggy to stress-test Illustrator to find all the bugs still lurking, I don’t know. She is probably one of only a few people outside of Adobe itself who regularly push the app to its limits.