Thanks, Sam.
That topic seems to be an old one that, coincidentally, has the same name. I’ll look into the database slug, though. If I find that it has a question mark in it, is it safe to delete the character (and modify the database directly)?
EDIT: I checked the database and the slug does not contain a question mark. Here are some details that may or may not help, though:
The title of the thread “Buttons ?” is identical (right down to the space before the question mark) to another post. The slugs for the two posts are “buttons-” and “buttons–1”.
Is there anything I can do to the database in the meantime to fix the error. (Say, manually change the slug to something else?) Since this is a live support site, I don’t want to leave this thread broken, but I don’t want to risk breaking the site either.