This is probably a pretty corner-y corner case, but trying to submit a question with a self answer behaves kind of badly if the post fails validation. I noticed it when I accidentally left off a required meta tag on a Q&A I was posting on another meta site, but it also applies to untagged posts and ones that are too short for the minimum character count on any site (meta or main), so I'd guess any other validation would cause it (new user restrictions and such).
What basically happens is that the validation error appears as you would expect, but then the entire answer box gets hidden, which initially caused me to think I may have lost all of my work:
Unchecking the "Answer your own question" box and then re-checking it brings back the answer box and all of the text in it. I'd guess this doesn't happen all that often, but when it does (as it did to me) it's pretty jarring.
Upon testing multiple browsers, I find that it is reproducible on Opera, but it is not reproducible on Chrome or Firefox.