If jgroups is installed at application server lib directory, a classloader leak will occur. When web app is undeployed, static classCache in ContextObjectInputStream will still refer those web app classes preventing web app to undeploy properly.

I think proper fix would be to remove this caching completely.

Additionally, it might be worth to check the current version form jboss: http://fisheye.jboss.org/browse/JBossCommon/common-core/trunk/src/main/java/org/jboss/util/stream/MarshalledValueInputStream.java#2904. It has some fixes for java 6.