Just log out, get kicked or lose connection when server restarts. Log back in, and the charakter is gone.
EDIT 15.08.14 23:24 GMT+1: some charakters who vanished just reappeared
EDIT 18.08.14 14:57 GMT+1: 2 of 3 times I start with a new character and in 50% of those cases when I die or relog my old character returns
EDIT 21.08.14 09:38 GMT+1: all my characters reappeared, don't ask my how