It happened multiple times now that I just pressed "Reply" on a PM but didn't notify that I replied to a PM of myself. After sending it it is undetectable, and it is really annoying to create that PM again.
My suggestion: either deny PM to sender itself or simply put it into the inbox.
PM to myself
Re: PM to myself
Yep. face this issue often. Better on press Reply check who is sender. Is sender is self, then swap sender and recipient, so in next code used recipient, not sender.