In fact, you join a server, and by doing something really simple you leave it before playing, then you re join the server and then you move backward and well played, you see yourself, you can kill him and you can steal your stuff. Even by doing that, you won't die and you'll get your stuff, no problem.
Really a game breaking bug, duplicate all your stuff is really broken. I've readed this bug on the internet.
It's even possible with the bug to have 5 clones of yourself with your stuff.
And MAYBE(not sure at all for this information/!\) it's working even better with a server with lags (like 150+ ping, but even with low ping no problem to do this bug)