Its the servers being derp as hell. If you lagged, didn't notice it & stayed on that's what did it. Only fix? Waiting for next server maint or hope your world crashes enough to rolling restart the servers (Bera did last week). I got it last week & well yeah its not fun at all.
You can whisper the char like its on. You can /find them and it will show you what channel its in... once ur on same chan /find doesn't work. yah.