Dave Lawrence

My tests confirm this is still present in 1.7.4

And the first line of Main.main(String[]) is
System.setProperty("java.net.preferIPv4Stack", "true");

so that pretty much makes anything the launcher does irrelevant.

I don't think I can edit affected versions though.

and anyway, since when did "Prefer IPv4" equate to "Don't use IPv6 at all"?

If Mojang do not agree to re-enable support by default then I would request that there at least be an option to switch IPv6 support back on again manually - without having to make code modifications.

I actually e-mailed the IPv6 Tunnel broker SIXXS a while back and pointed out to them that Minecraft works in IPv6 and they added it to their "Cool IPv6 stuff" page http://www.sixxs.net/misc/coolstuff/

but it seems now Minecraft is back in the 1990s

The behaviour can be seen in Java outside of Minecraft:

System.out.println (java.net.InetAddress.getLocalHost().toString());

which prints different IP addresses according to the various circumstances already described (ie Windows vs Linux and modified /etc/hosts)

Should the localhost issue be reported as a separate bug, seeing as it is, well totally separate to the bug mentioned in the title.
It DOES matter to which IP the server is bound because the IP specifies the interface and localhost is not the same interface as Ethernet. Services which are bound to all interfaces are shown in netstat with a * instead of an IP address. Also you talk about binding to *:25565 - that's the server, the client's publish-to-LAN functionality doesn't use that port.
I have discovered some more about this that may be a work-around to Linux users and possibly a clue to developers: The IP address selected is the one associated with the hostname, as returned by the command line ("hostname"). And this may be affected by your hosts file (/etc/hosts). So for instance I had the following in my hosts file (/etc/hosts)

127.0.0.1 localhost
127.0.1.1 westy3
These lines were written by the OS installer, and westy3 is the name I gave that computer at install time. Minecraft was binding to the second address. I now comment out the westy3 line like so
127.0.0.1 localhost
#127.0.1.1 westy3

and the problem is fixed. Some more command output for your info:
dave@westy3:/opt/minecraft$ hostname
westy3
dave@westy3:/opt/minecraft$ host 127.0.1.1
Host 1.1.0.127.in-addr.arpa. not found: 3(NXDOMAIN)
dave@westy3:/opt/minecraft$ host 172.20.21.103
103.21.20.172.in-addr.arpa domain name pointer westy3.
dave@westy3:/opt/minecraft$

You see now the computer name is associated with a LAN address (a Bluetooth connection as it happens) and hey presto, Minecraft's publish-to-LAN now binds to this address. (At some point I'll confirm on a real LAN that this makes the game accessible, but I'm 99% certain it will).