I have noticed these posts before but I don't have the answer. My guess is that when someone went back to edit their post, they did so in HTML mode and messed with the code by erasing or adding something in the code line. This would have made the code not function properly and therefore you see the leftover bits of the code when the edited post is displayed.

Ed, you posted while I was typing. I just tried to reproduce the quirk by editing in HTML mode using the firefox browser, but I can't get it to go. Must be something  with HTML for sure, but where, when and how , I don't know.

As long as you can read the post, the world will go on.