Trying to continue with the same session id on different jboss instance and web browser leads to the following exception on the instance's console:
12:41:21,767 WARN [SessionBasedJBossCacheService] Problem accessing session data : class java.lang.NullPointerException null

Steps to reproduce:
1) download jboss-6.0.0.M1 (for example from http://reports.qa.atl.jboss.com/release_tests/binaries/JBossAS/jboss-6.0.0.M1.zip)
2) unzip it twice to different folders
3) run the first instance from its bin directory: ./run.sh -c all -g DocsPartition -u 239.255.101.101 -b localhost -Djboss.messaging.ServerPeerID=1 -Djboss.service.binding.set=ports-default
4) run the second instance from its bin directory: ./run.sh -c all -g DocsPartition -u 239.255.101.101 -b localhost -Djboss.messaging.ServerPeerID=2 -Djboss.service.binding.set=ports-01
(after a while both instances know about one another ( All Members of cluster = 2))
5) edit examples/jsf/numberguess/src/main/webapp-jboss5/WEB-INF/web.xml (add <distributable/> as its first tag so that the application.....is enabled for a cluster environment ( !!! I don't know for sure if it is enough, maybe this is the problem !!!)
6) run mvn package in examples/jsf/numberguess
7) copy resulting war file (weld-numberguess.war) from numberguess/target/ directory to serve/all/farm directory at first jbossAS instance
8) remove cookies for "localhost" domain from web browser, disable cookies
9) go to http://localhost:8080/weld-numberguess/home.jsf, play for 2-3 times with application (try to guess a number)
10) copy&paste the url (for example "http://localhost:8080/weld-numberguess/home.jsf;jsessionid=VBobYX3Itd9fUI-qXhcucw__") into another window with cookies disabled, change port number from 8080 to 8180 and go to the page
11) now you can see the exception in the second jboss instance's console and the application behaves like it doesn't know this session and starts from scratch