FreeBSD’s pf has serious problems with ipv6 fragment handling. The problems cascade into other issues like named axfr time outs. Add this, “pass proto ipv6-frag all”, to your ruleset somewhere near your antispoof rules to fix this.
Much of the issue is that the FreeBSD team has diverged their version of the pf firewall so far from the OpenBSD version that they cannot incorporate upstream fixes. I’m not making my situation any better by sticking with FreeBSD 9. Some of this is probably addressed in FreeBSD 10.
While this persists the best course of action is probably to make sure it works on OpenBSD first, then figure out how to deal with any FreeBSD issues.