Old problem revisited, NAT+ICMP (PMTUD).. not yet commited all

I'm seeing a problem in FreeBSD 5-STABLE that looks suspiciously like
NetBSD PR kern/10993. It seems this may also be referenced as
FreeBSD PR bin/78424 which I've asked about on the FreeBSD -stable
mailing list earlier today, with no replies as yet.

Specifically what I'm seeing are transfers between a windows machine
behind a FreeBSD NAT, and other machines out on the internet,
randomly failing when the windows box has PMTUD enabled. The ICMP
NEEDFRAG's aren't being NATed by the FreeBSD box as they should be,
which is using ipfw as a firewall and ipnat from ipfilter as the NAT,
and so connections eventually just die off as the windows machine
tries to send large-window packets, and never sees the ICMP replies
destined to it.

I'm wondering if this NetBSD PR is still outstanding or if the PR
database is just stale, and if so, where I might be able to get a
diff of the appropriate file(s) to apply to my FreeBSD box to fix the
problem? Having this as a kernel bit in FreeBSD under the contrib
tree makes me rather wary of following the "try the one in -current"
instructions from the NetBSD PR.

Any ideas?