The JBossCache based session clustering mechanism allows each individual node in the cluster to independently expire the instance of the session resident on that node. This results in multiple HttpSessionEvents being generated for the same logical session, which causes problems in some use cases.

An example of how this causes problems reported by an end user:

"This is a sensitive issue for us since we hold a legacy lock on resoures for the duration of a session and we use the session unbind event to release that resource. Obviously when multiple servers execute this release for one session [near] simultaneously, we see some messy error messages."

I can imagine other use cases where the existing behavior might be desired, i.e. a listener being registered on each node where the session has been accessed in order to do some local cleanup, so the expiration behavior will probably need to be configurable.