User X recently edited their post (which has been closed) and wrote in the edit summary something rude (not too rude, but not nice) about those who closed the post. So I (a mod on that site) simply edited it out.
However, if you go to User X's activity page under revisions, the rude edit summary persists and anyone can see it.
This seems like a bug. The whole point of editing it out is so it's gone.