bridging and ipfw under 5.4-RC3.

I'm having a bit of trouble getting ipfw and bridging working under
5.4-RC3.  I've just upgraded a 4.11 machine to RELENG_5_4 expecting the
preexisting bridging configuration to work, but it doesn't.  Or at least
it does at boot time and then after a little while bridging just stops
altogether.  If I kldunload bridge and ipfw and then reload them I can
get it working again, but only for a short period.  Does anyone else see
this too or is it just me?

sysctl.conf:
    net.link.ether.bridge.enable=1
    net.link.ether.bridge.ipfw=1
    net.link.ether.bridge.config=fxp0,fxp1

rc.conf:
    firewall_enable="YES"
    firewall_script="/etc/rc.firewall-ours"
    firewall_type="ours"

(The firewall rules aren't the problem here...)

Any ideas how to debug this?
Joe
-- 
Josef Karthauser (joe_at_tao.org.uk)	       http://www.josef-k.net/
FreeBSD (cvs meister, admin and hacker)     http://www.uk.FreeBSD.org/
Physics Particle Theory (student)   http://www.pact.cpes.sussex.ac.uk/
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