I ran into an issue earlier today where I tried to comment on someone's post to indicate they should make sure they used an @2x and @3x image (iOS stackoverflow question). I was then shown a dialog saying I could only reference / reply to one user at a time. I had to delete one of the @ symbols to be able to post my comment. There were no users I could reference named 2x or 3x, so why was I shown this message? Although a small one, is this a known issue?