As Faint said, the 'You can't Leave yet' message is only to prevent you from dim hopping very fast, which is how users in the past duplicated items. But it that aside, I've never heard of a glitch where you can see a duplicate of yourself. Maybe someone took your user name, but inserted a space before or after the username, which would make it seem like the same username. If that is the case, shoot me a PM and we can discuss the matter further
