Discussion related to https://jira.jboss.org/jira/browse/JBAS-7745
Eric, I can't reproduce this, using either 5.1.0.GA or my local build of the EAP 5.0 maintenance branch.
One thing I noticed is in the JIRA description, the jvmRoute appended to session id's remained the same even after your comments indicated you should have switched servers. It's always ESAJBOSS3_jboss_172.30.4.76_1. Did you inadvertently configure the same jvmRoute on both servers?
If you want to explore further, edit conf/jboss-log4j.xml to enable TRACE logging from categories org.jboss.web.tomcat.service.session and org.jboss.cache and attach the server.xml from the surviving node. (The portion from when you start making requests on the cluster.
BTW, I found I couldn't deploy this war on a current build of the AS. I'll file a JIRA for that.
You attached a doc to the JIRA that AFAICT shows the same thing as the original description, except that the jvmRoute changes between the 2 servers now. So that rules that out as an issue.
But, like I said, I can't reproduce this. So, to move forward I'll need the detailed logging I mentioned.