Comment 3 for bug 686265

It looks to me like apt-avahi-discover is broken for IPv6, as it tries to parse out the IP address, and then sets its results to "$IP:$PORT". For IPv6, it should be "[$IP]:$PORT". Not sure if my implementation is the ideal way to detect IPv4 versus IPv6, but here's a diff attempting to fix this. Try it out (I don't actually know the output format for avahi-browse, and don't have the proxy set up on my machine, so I don't know for sure this thing works).

Apply this against apt-avahi-discover, and see if you get better results.