alt Hacker NewsLocalhost doesn't appear on autodiscovery. Whatever you ran into had nothing to do with IPv6, but rather with your application not binding to the address you were telling it to bind to. On IPv6, localhost binds to ::1, not anything reachable by any other address. Furthermore, whatever you set up automatically seems to have added itself to your server's firewall, which is equally troubling.
The address my clients were finding automatically was a link-local address (fe80...). Can't say exactly what happened but it was very surprising since I didn't even know these addresses existed.
I'm sure it's totally my fault but that's the point: folks who know how ipv4 works may have huge blind spots for ipv6.