One possibility is that your machine is unable to make IPv6 DNS
requests, and that they time out rather than succeeding or failing
quickly, perhaps due to a broken upstream resolver/nameserver.
It may be that some timer expires in sshd before this completes.

I've been using 1.6 on networks with and without IPv6 service, and
seen quick 'no route to host' for v6 addresses.

-- 
        Greg Troxel <gdt@ir.bbn.com>