Why are there "Unresponsive EPR" in the log during calls to a service when the server restarts - threads BLOCKED in JmsConnectionPool.getSession?

Issue

• Log is displaying "Unresponsive EPR":

2012-08-08 18:11:01,196 INFO  (pool-18-thread-7:) Unresponsive EPR: JMSEpr [ PortReference < <wsa:Address jms:192.168.1.123:1099#SampleQueue/>, <wsa:ReferenceProperties jbossesb:java.naming.factory.initial : org.jnp.interfaces.NamingContextFactory/>, <wsa:ReferenceProperties jbossesb:java.naming.provider.url : 192.168.1.123:1099/>, <wsa:ReferenceProperties jbossesb:java.naming.factory.url.pkgs : org.jnp.interfaces/>, <wsa:ReferenceProperties jbossesb:destination-type : queue/>, <wsa:ReferenceProperties jbossesb:destination-name : SampleQueue/>, <wsa:ReferenceProperties jbossesb:specification-version : 1.1/>, <wsa:ReferenceProperties jbossesb:connection-factory : ConnectionFactory/>, <wsa:ReferenceProperties jbossesb:persistent : true/>, <wsa:ReferenceProperties jbossesb:acknowledge-mode : AUTO_ACKNOWLEDGE/>, <wsa:ReferenceProperties jbossesb:transacted : false/>, <wsa:ReferenceProperties jbossesb:type : urn:jboss/esb/epr/type/jms/> > ] for message: header: [  ]

• We have made a "kill -3 <pid>" over the JBoss server and there are 100 threads BLOCKED as you can see:

"pool-18-thread-100" prio=3 tid=0x0000000102cb1000 nid=0x4bf waiting for monitor entry [0xfffffffe8ee7a000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at org.jboss.internal.soa.esb.rosetta.pooling.JmsConnectionPool.getSession(JmsConnectionPool.java:190)
        - waiting to lock <0xfffffffefceea3a8> (a org.jboss.internal.soa.esb.rosetta.pooling.JmsConnectionPool)
        at org.jboss.internal.soa.esb.couriers.JmsCourier.getJmsSession(JmsCourier.java:159)
        - locked <0xffffffff04f63eb8> (a org.jboss.internal.soa.esb.couriers.JmsCourier)
        at org.jboss.internal.soa.esb.couriers.JmsCourier.createMessageProducer(JmsCourier.java:383)
        - locked <0xffffffff04f63eb8> (a org.jboss.internal.soa.esb.couriers.JmsCourier)
        at org.jboss.internal.soa.esb.couriers.JmsCourier.internalDeliver(JmsCourier.java:209)
        - locked <0xffffffff04f63eb8> (a org.jboss.internal.soa.esb.couriers.JmsCourier)
        at org.jboss.internal.soa.esb.couriers.JmsCourier.deliver(JmsCourier.java:181)
        at org.jboss.internal.soa.esb.couriers.TwoWayCourierImpl.deliver(TwoWayCourierImpl.java:189)
        at org.jboss.soa.esb.client.ServiceInvoker$EPRInvoker.attemptDelivery(ServiceInvoker.java:576)
        at org.jboss.soa.esb.client.ServiceInvoker$EPRInvoker.access$200(ServiceInvoker.java:493)
        at org.jboss.soa.esb.client.ServiceInvoker.post(ServiceInvoker.java:343)
        at org.jboss.soa.esb.client.ServiceInvoker.deliverAsync(ServiceInvoker.java:233)
        at org.jboss.soa.esb.services.jbpm.actionhandlers.EsbNotifier.execute(EsbNotifier.java:137)
        at org.jbpm.graph.def.Action.execute(Action.java:117)

• 100 are the number of threads in the service - the one that is sending the signal "Unresponsive EPR" when called.