zombie screen / irc difficulties

hey there,

today I was unable to log into my private irc server. Really strange, since I changed nothing, the server was still running and all. Also my screen session seemed to have vanished.
After I asked another user I heard I was still in the channel... somehow my screen session was off the radar but still running, so I could not connect to it. Also since in this session I already was logged into the irc server, I could not log in again.
Well, killing the session and opening a new one was easy, but had I not asked my friend I could have been debugging for days without ever getting the idea I would still be logged in from somewhere.
So, every detail matters, even a "crashed" screen session :D