I see that you have it back ported to 5.1 and new release 5.1.8 was released. So I have it tested. But unfortunately it still not working properly.
[kamailio.log](https://github.com/kamailio/kamailio/files/3068985/kamailio.log) [lb-sip.zip](https://github.com/kamailio/kamailio/files/3068988/lb-sip.zip)
It works perfect when I move this handler to kamailio.cfg like: event_route[topos:msg-outgoing] { if($sndto(ip)=~"^10.") { drop; } }