When a EJB2.x MDB is deployed in JBoss4.x and 5, there are some additional (JBoss specific) MBeans registered. For ex: An MBean to stop/start delivery of messages to the MDB.
http://anonsvn.jboss.org/repos/jbossas/trunk/server/src/main/org/jboss/ejb/MessageDrivenContainer.java
// Try to register the instance pool as an MBean try { ... } catch(Throwable t) { log.debug("Failed to register pool as mbean", t); } // Initialize pool instancePool.setContainer(this); instancePool.create(); for (Iterator it = proxyFactories.keySet().iterator(); it.hasNext();) { String invokerBinding = (String) it.next(); EJBProxyFactory ci = (EJBProxyFactory) proxyFactories.get(invokerBinding); // Try to register the container invoker as an MBean try { .... }