Mac OS X Leopard firewall issues

I’ve been running nginx on MacOS X 10.5 (Leopard), mostly without
issues. But the firewall is really giving me a headache right now and
my google searches haven’t turned up a solution. For the past year or
so, nginx has been listed as an application allowed to accept incoming
connections and it has worked fine. But after a reboot two days ago,
when the firewall is on, nginx is not allowed to accept connections,
even though it is still explicitly allowed to in the firewall system
preference panel.

Has anyone else had this particular headache before? Is there a way to
solve it other than turning the firewall off completely? (Something
I’d really like to avoid).