One  thing observed  with jboss 7.2 , when slave node is receiving application requests and thats goes down session is replicated to master Node without any issues.

But if application requests are serving by Master Node , and that went down then there is no session replication.

Gives the error 

[Server:server-six] 06:53:43,684 ERROR [org.apache.catalina.connector] (ajp-/192.168.8.153:8259-12) JBWEB001018: An exception or error occurred in the container during the request processing: java.lang.NullPointerException

Thanks,

Mahesh