what i did wrong?

i have :

block in on ppp0 proto udp all

pass in quick on ppp0 proto udp from any to 217.96.12.12 port = 518
pass in quick on ppp0 proto udp from any port = 518 to 217.96.12.12


in /etc/ipf.conf (and many other lines but only these 3 are about udp).

when i got talk request from user@another-host and answer it all works.
But when i first request talk and user@another-host answers - connection
isn't established but talk request are shown instead.

what i did wrong?