Form what I found in http://lists.kamailio.org/pipermail/devel/2008-August/015080.html, it seems to me that it's a bug that kamailio adds received=IP parameter although force_rport was not called.
2009/7/16 catalina oancea catalina.oancea@gmail.com:
Hello,
Does anybody know how to disable the received=IP Via parameter that is added by default from kamailio? For the case I want to disable it in, I have no NAT handling. Also, I have: dns=no rev_dns=no
Anything else?
Thanks Catalina