This user has been vandalising (but not deleting) his/her own questions. He/she has edited the questions, wiped out the title and all the text, and replaced it with "deleted question".

Is there any policy in place regarding this kind of behaviour? Is it allowed at all?

I've rolled back all the vandalising edits, out of respect for the users that took the time to answer, and then flagged one of the questions for moderator attention. But I don't know if this is the right thing to do.