It happened with a wierd combination of my friend's email and my autopass or my email with his pass (we both play on the same computer) and he cancelled the login when it was loading. After this, he logged with his email/pass. There were all our characters on the same screen and if you watch on the down side of the screen you'll see "15 of 11 slots used" : he has 11 slots with 11 chars and I have 4 chars. Funny picture.
http://hereticbutcher.free.fr/gwguru/bug.JPG
EDIT: Picture too large. Please read the forum Sticky threads for rules on picture sizes and how to change them. - Swampgirl
Funny bug with character selection screen
tipiak