Upgrade to 14.4 and vtnet+NAT stopped working

Hello.

I've just upgraded a 14.3 virtual server to 14.4 and some part of 
networking has stopped working.
I'm sure I've missed some change in release notes, upgrade instructions, 
whatever... but I cannot find the reason.

I've got:
_ WAN interface: vtnet0;
_ epair0a as 192.168.x.1;
_ epair0b as 192.168.x.2 (used by a VNET jail);
_ ipfw that NATs 192.168.x.2, so that it can connect to the outside world.

Everything used to work with 14.3.
Now that I upgraded to 14.4:
_ base works normally and can connect to the Internet or receive 
incoming connections (over vtnet, of course with no NAT needed);
_ base can connect to services inside the jail;
_ jail can ping the world (i.e. ping 8.8.8.8 works, so NAT, at least 
partially, works);
_ however no TCP or UDP gets from the jail to Internet!



For example, if inside the jail I issue:
> # host www.google.it 8.8.8.8
> ;; connection timed out; no servers could be reached

ipfw shows nothing was blocked.
tcpdump on vtnet shows the query packet getting out to 8.8.8.8, but no 
answer coming in.
What's strange is that this packet is 0 bytes long!

This also happen if I "telnet x.y.z.w port" (and on the other side I can 
confirm I get zero length packets).


I tried putting "hw.vtnet.csum_disable=1" in /boot/loader.conf, but it 
didn't help.

What should I check?

  bye & Thanks
	av.