Just to expand on this idea, as it's definitely what I think happened... The student may not have had to spend 19 minutes writing. it's possible they had the discussion board loaded at 4:11pm and were reading through it, then decided to reply to the post that had already been deleted. I *think* since they have the discussion page loaded that they'd be able to reply to any post that was already loaded on their screen at that point. Think about it from the student aspect, if they did work and went to submit and were given an error, they'd likely feel they were cheated by the system, so this way probably makes the most sense even if it leaves a bit of a messy look.
Hope this helps a bit more.
-Chris