Actually, I was only half-joking. gmail is a pop account, so if there is another computer logged into your gmail account, things can get dicey. Hence the "if you open a mailbox that is already in use..." warning. I was just guessing that either Satan or your ex-girlfriend are using a Dell computer (dell5160) and have logged into your gmail account and are mucking around in your Deleted Items folder.
Impossible you say?!