Comments less than 15 characters are rejected, but in some cases (e.g. "link?") it often looks silly to tack on more writing just to pad it out. Up until now, I'd just add 10 spaces before the '?' but that doesn't seem to work anymore.
The 15 character comment minimum has actually been put in place just to prevent short comments as the ones you're referring to. They're nothing more than noise. If you can't say it in more than 15 chars, it probably shouldn't be said.