HELP! Does not work correctly dummynet or IPFW !!!

[Maxim]

Hi!

Ran into such problem, when FREEBSD 5.2.1 used and dummynet
was all ok, then FREEBSD 5.4 set and noticed track problem,
at creation: ipfw add 100 pipe 10 ip from any to any out via xl0
governed the fragmented packages do not pass,
at such rule all works ok: ipfw add 100 pipe 10 ip from any to any in via xl0.

Problem is observed, if a package passes through router.

What a problem can be in?

With the best wishes,
Maxim.