6.4: IPv6 and syslogd/named

Hello FreeBSD friends,

After upgrading from 6.3 to 6.4-RELEASE,
I find that syslogd and named no longer start after rebooting.
I can manually run "/etc/rc.d/syslogd start" to start syslogd
after boot, and it also applies to named.

After doing some experiment, I find that removing ipv6_enable=YES
from /etc/rc.conf solves this issue, but of course it is not what
I want, so I have to start the two daemon manually now.

This machine is IPv4/v6 dual stack using 6to4, but disabling just
IPv6 forwarding, IPv4 address mapping (required by Java), rtadvd,
or 6to4 doesn't make syslogd/named start happily, I have to
disable IPv6 entirely. Does anyone know what may cause this?

Both syslogd and named have -4 and -6 flags (man syslogd, man named). Anything useful in there?
Are you using ppp?

echo rc_debug=YES >>/etc/rc.conf
And reboot. Anything useful in /var/log/messages then?