Session timeout in different JVM

Background Information
======================
Application Server: WebSphere Application Server with 2 JVMs created, server1 (port 9081) and server2 (port 9082)
Web Server: IBM HTTP Server, webServerX
Application: 2 applications, appA (installed in server1) and appB (installed in server2)

Problem Encountered
===================
User only need to login once in either appA or appB, then he can be redirected back and forth with sessionID as authentication key without furhter login action, i.e appA redirects to appB, then appB redirects back to appA. In both applications, I do the redirection by "location.replace(URL)". SessionID must be consistent through out user's operation, otherwise re-login is required.

At first, I code the redirection URL as http://sever1:9081/appA/aaa.jsp?key=sessionID and http://sever2:9082/appB/bbb.jsp?key=sessionID, it works fine in both applicaions. Later on, after I've updated the server plug-in in Web Server, I changed the redirection URL as http://webServerX/appA/aaa.jsp?key=sessionID and http://webServerX/appB/bbb.jsp?key=sessionID, then problem occurs. Whenever a redirection is triggered, the session in parent app will be killed immediately, although the child app can still function normally, it cannot be redirected back to parent app due to session ID lost.

Has anyone encountered the mentioned problem before? I'm really frustrated by this situation, would appreciate if someone could give me some advices, thousands thanks.

Regards...PS

You could manage the session manually with application logic instead of relying on the server's session mechanism, although it requires some work.

Which session item can I manually set in application logic? Please give me some hints, thank you so much.

Regards...PS

Store the session information in a database.