13.1: "ipfw forward" no longer works (after upgrade from 12.3)

Hija,

  I just upgraded from 12.3 to 13.1-STABLE, and now "ipfw forward"
gets ignored. 

I checked with:
  $ ipfw add 1 fwd 10.1.0.120 all from any to any out

I get an incrementing count there:
   # ipfw show 1
   00001   4101    782871 fwd 10.1.0.120 ip from any to any out
   # ipfw show 1
   00001   4117    785795 fwd 10.1.0.120 ip from any to any out

But nothing appears on the interface. The packets are allowed but
appear to take the default route.

Starting to look into details: this one doesn't work eitner
  $ ipfw add 1 fwd 10.1.0.120 all from any to any in

This one however, does work (but only for incoming packets):
  $ ipfw add 1 fwd 10.1.0.120 all from any to any

For the records:
   # sysctl -a | grep one_pass
   net.inet.ip.fw.one_pass: 0