A few days ago, I saw this answer, and thought nothing of the fact that it had <30 characters (including zero-width spaces and HTML tags and other Unicode characters). But then I saw this answer, which was also posted with less than 30 characters, and it reminded me. When I try to post something like that, I get:
That also shows if I try to edit in a single extra character, indicating there aren't any invisible characters. Why were these two posts allowed? Was it just a brief system fart?