We are testing our application on WLSS-3.1- MP1 by generating load with SIPp tool.
Our application sends out INVITE. Under load we see sometimes retransmission of the INVITE. From weblogic console logs, it looks container creates "Derived SIP session" for these retransmission.
The problem is when such derived session is created by container, the information that we put in SIP session is not available when response comes in to the retransmitted request.
Derived sessions are only created when container receives response(s) for initial request with different To header field Tag parameter value.
So you must be getting e.g 18x with to tag tag1 and 2xx with to tag tag2 .. Look for that .
Also there was a bug where in attributes were not copied from primary session into derived session. Bug number is CR372191.
Contact oracle support and ask for patch .