We are running into another issue with PUB/SUB breakages where subscribers are loosing connection. In a nutshell when a subscriber losses connection then there seems to be a TIME_WAIT state on the tcp connection on the PUB end and messages are not getting through.
This is only being reported by a single Salt user at this point, and the discussion can be found here:
At least this is where I think we are finally getting to some meat.
Looks like a TCP/IP level problem.
I don't think libzmq can do a lot about it.