[SR-Users] T.38 fax, rtpproxy, re-invite

Hello. I'm using almost default kamailio.cfg with nathelper, rtpproxy, PSTN dialing and other default features. I have following scheme:

FXS gateway -> (NAT) -> Kamailio -> FreeSwitch

Voice calls work perfectly, no one-direction sound and so on.

But with fax machine there was a problem. In wireshark I saw UDPTL from FS to Kamailio IP, and no UDPTL at all to FXS gw. I've guessed that something's wrong with a re-INVITE request processing in Kamailio. I've added this to WITHINDLG route:

else if ( is_method("INVITE") ) { record_route();

}

And problem was magically solved, T.38 now works OK. Is this OK solution or this may break something elsewhere?

Thanks.