To see this, start the server, deploy an ejb jar, undeploy the ejb jar. At this point, actually, the pool is undeployed and can't be seen e.g. in the JMX console. But if now you shutdown the server in the logs for each previously deployed and undeployed EJB there will be an exception (logged at DEBUG though)

2009-04-07 23:20:24,367 DEBUG [org.jboss.system.ServiceCreator] (JBoss Shutdown Hook) Error unregistering mbean jboss.j2ee:service=EJB,plugin=pool,jndiName=cmp2/audit/AuditSession
javax.management.InstanceNotFoundException: jboss.j2ee:service=EJB,plugin=pool,jndiName=cmp2/audit/AuditSession is not registered.
at org.jboss.mx.server.registry.BasicMBeanRegistry.get(BasicMBeanRegistry.java:526)
at org.jboss.mx.server.MBeanServerImpl.unregisterMBean(MBeanServerImpl.java:383)
at org.jboss.system.ServiceCreator.uninstall(ServiceCreator.java:323)
at org.jboss.system.microcontainer.OnlyUnregisterAction.uninstallAction(OnlyUnregisterAction.java:45)
at org.jboss.system.microcontainer.OnlyUnregisterAction.uninstallAction(OnlyUnregisterAction.java:35)
at org.jboss.dependency.plugins.action.SimpleControllerContextAction.simpleUninstallAction(SimpleControllerContextAction.java:79)
at org.jboss.dependency.plugins.action.AccessControllerContextAction.uninstall(AccessControllerContextAction.java:131)
at org.jboss.dependency.plugins.AbstractControllerContextActions.uninstall(AbstractControllerContextActions.java:58)
at org.jboss.dependency.plugins.AbstractControllerContext.uninstall(AbstractControllerContext.java:354)
at org.jboss.dependency.plugins.AbstractController.uninstall(AbstractController.java:1664)
at org.jboss.dependency.plugins.AbstractController.uninstallContext(AbstractController.java:1275)
at org.jboss.dependency.plugins.AbstractController.uninstallContext(AbstractController.java:1179)
at org.jboss.dependency.plugins.AbstractController.uninstall(AbstractController.java:655)
at org.jboss.dependency.plugins.AbstractController.uninstall(AbstractController.java:568)
at org.jboss.system.ServiceController.shutdown(ServiceController.java:602)
at org.jboss.system.server.jmx.JMXKernel.shutdownServices(JMXKernel.java:408)
at org.jboss.system.server.jmx.JMXKernel.stop(JMXKernel.java:256)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.jboss.reflect.plugins.introspection.ReflectionUtils.invoke(ReflectionUtils.java:59)
at org.jboss.reflect.plugins.introspection.ReflectMethodInfoImpl.invoke(ReflectMethodInfoImpl.java:150)
at org.jboss.joinpoint.plugins.BasicMethodJoinPoint.dispatch(BasicMethodJoinPoint.java:66)
at org.jboss.kernel.plugins.dependency.KernelControllerContextAction$JoinpointDispatchWrapper.execute(KernelControllerContextAction.java:241)
at org.jboss.kernel.plugins.dependency.ExecutionWrapper.execute(ExecutionWrapper.java:47)
at org.jboss.kernel.plugins.dependency.KernelControllerContextAction.dispatchExecutionWrapper(KernelControllerContextAction.java:109)
at org.jboss.kernel.plugins.dependency.KernelControllerContextAction.dispatchJoinPoint(KernelControllerContextAction.java:70)
at org.jboss.kernel.plugins.dependency.LifecycleAction.uninstallActionInternal(LifecycleAction.java:249)
at org.jboss.kernel.plugins.dependency.InstallsAwareAction.uninstallAction(InstallsAwareAction.java:157)
at org.jboss.kernel.plugins.dependency.InstallsAwareAction.uninstallAction(InstallsAwareAction.java:42)
at org.jboss.dependency.plugins.action.SimpleControllerContextAction.simpleUninstallAction(SimpleControllerContextAction.java:79)
at org.jboss.dependency.plugins.action.AccessControllerContextAction.uninstall(AccessControllerContextAction.java:131)
at org.jboss.dependency.plugins.AbstractControllerContextActions.uninstall(AbstractControllerContextActions.java:58)
at org.jboss.dependency.plugins.AbstractControllerContext.uninstall(AbstractControllerContext.java:354)
at org.jboss.dependency.plugins.AbstractController.uninstall(AbstractController.java:1664)
at org.jboss.dependency.plugins.AbstractController.uninstallContext(AbstractController.java:1275)
at org.jboss.dependency.plugins.AbstractController.uninstallContext(AbstractController.java:1179)
at org.jboss.dependency.plugins.AbstractController.uninstall(AbstractController.java:655)
at org.jboss.dependency.plugins.AbstractController.uninstall(AbstractController.java:568)
at org.jboss.kernel.plugins.deployment.AbstractKernelDeployer.undeployBean(AbstractKernelDeployer.java:394)
at org.jboss.kernel.plugins.deployment.AbstractKernelDeployer.undeployBeans(AbstractKernelDeployer.java:373)
at org.jboss.kernel.plugins.deployment.AbstractKernelDeployer.undeploy(AbstractKernelDeployer.java:162)
at org.jboss.kernel.plugins.deployment.BasicKernelDeployer.undeploy(BasicKernelDeployer.java:88)
at org.jboss.bootstrap.microcontainer.TempBasicXMLDeployer.undeploy(TempBasicXMLDeployer.java:98)
at org.jboss.kernel.plugins.deployment.BasicKernelDeployer.shutdown(BasicKernelDeployer.java:102)
at org.jboss.bootstrap.microcontainer.ServerImpl.doShutdown(ServerImpl.java:186)
at org.jboss.bootstrap.AbstractServerImpl.shutdownServer(AbstractServerImpl.java:589)
at org.jboss.bootstrap.AbstractServerImpl$ShutdownHook.run(AbstractServerImpl.java:909)