Comment 13 for bug 284874

I noticed on a newly installed Lucid box that this was still the case. Exacerbating the problem for me was that I enabled ufw, but forgot to set 'IPV6=yes' in /etc/default/ufw. This blocked any ipv6 config packets and thus caused the failure of any ipv6 configuration. The default ipv6 firewall is pretty strict. After enabling the ipv6 firewall, which allows the appropriate packets in, my network was configured properly again with a dual stack.

But the situation still exists where I take my machine to a location that doesn't have any ipv6 routers and it fails to keep the ipv4 config.