I've spent a bit of time looking at the history, and found another 
error.

Basically, recent programmers assumed that the net_host is a superset 
of net_domain.  In reality, they are two separate fields in the menu, 
and not related at all!

See get_ifinterface_info: 
                        /* split hostname into host/domain parts */
                        size_t max_len = dot - hostname;
                        max_len = (sizeof(net_host)<max_len)?sizeof(net_host):max_len;
                        *dot = '\0';
                        dot++;
                        strncpy(net_host, hostname, max_len);
                        max_len = strlen(dot);
                        max_len = (sizeof(net_host)<max_len)?sizeof(net_host):max_len;
                        strncpy(net_domain, dot, max_len);

And config_network:

        msg_prompt_add(MSG_net_domain, net_domain, net_domain, STRSIZE);
        msg_prompt_add(MSG_net_host, net_host, net_host, STRSIZE);

Therefore, 

        /* Write hostname to /etc/rc.conf */
        if ((net_dhcpconf & DHCPCONF_HOST) == 0)
                add_rc_conf("hostname=%s\n", net_host);

*NEVER* has the domain part!


Unfortunately, note the comparisons here:

/*
 * write the new contents of /etc/hosts to the specified file
 */
static void
write_etc_hosts(FILE *f)
{
        int l;

        scripting_fprintf(f, "#\n");
        scripting_fprintf(f, "# Added by NetBSD sysinst\n");
        scripting_fprintf(f, "#\n");

        scripting_fprintf(f, "127.0.0.1 localhost\n");

        scripting_fprintf(f, "%s\t", net_ip);
        l = strlen(net_host) - strlen(net_domain);
        if (l <= 0 ||
            net_host[l - 1] != '.' ||
            strcasecmp(net_domain, net_host + l) != 0) {
                /* net_host isn't an FQDN. */
                scripting_fprintf(f, "%s.%s ", net_host, net_domain);
        }
        scripting_fprintf(f, "%s\n", net_host);
}

This code is completely bogus, since the net_host never has the 
net_domain in it.  But it works (on bad assumptions), because  
net_host[l - 1] != '.' is always true!
-- 
William Allen Simpson
    Key fingerprint =  17 40 5E 67 15 6F 31 26  DD 0D B9 9B 6A 15 2C 32