Being Disconnected From Client but not from Game

So, I seemed to have found a really, really odd bug. I don't know any of the reproduction steps or anything, but it seems a user can be logged out from the client yet not be so from the game. How did I find this out, you may ask? Well, it seems like someone hacked into my account, I noticed that I was logged out, immediately changed my password and whatnot, reconnected to the client . . . but could not enter the game and the user was still playing the game that he was in when he hacked into my account. (The good news is that he won, but this is seriously a very interesting bug)