Yeah, I'm having the same problem.  I was connected, and i was surprised when i came back to find nobody else was in the server with me.  I got out of it to go eat, and when i came back, I tried to get into the same server using the Custom Client, but the select server screen froze.  I tried to connect the regular way, but it just took me straight to single player.  Any help, guys?

EDIT: Other servers work, just not WOM