U 2010/02/05 09:06:32.497347 10.100.0.101:5062 -> 10.0.255.10:5061 INVITE sip:12345@10.0.255.10:5061 SIP/2.0. Contact: sip:45400@10.100.0.101:5062.
So this is the invite from the calling party to openser
U 2010/02/05 09:06:32.521248 10.0.255.10:5061 -> 10.100.0.106:5065 INVITE sip:12345@10.100.0.106:5065 SIP/2.0. Contact: sip:45400@10.0.255.10:5060.
And this is the invite from openser to the called party.
The Contact is rewritten to openser. I don't see how this is causing a problem. The issue seems to arrive later when the ACK doesn't get picked up.
Regards
Jon