network of broker does not work properly where there are more than 1 message producer

[hh_meta]

I tried to configure a network of broker for distributed queue within Spring
2.0. 
So I have 4 brokers in total:
Broker1 and Broker2,  both have a message producer on them;
Broker3 and Broker4,  both have a message consumer on them.
The idea is message produced from either Broker1 and Broker2 will be passed
to consumers on Broker3 or Broker4, load-balanced and supports failover.
here is the activemq.xml for all these brokers, each broker uses a different
tcp port # since I run all 4 brokers on one machine, and I'm using ActiveMQ
4.1.1 release:
<beans>
  <bean
class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"/>
  <broker name="embedded_broker" useJmx="false" 
xmlns="http://activemq.org/config/1.0"; persistent="false" 
destroy-method="stop">
 
<!-- define a discovery uri for dynamic broker lookup --> 
<!-- prefetch is set to 1 to make sure load balancing during 1:1 testing, we
should change that in production env for better performance -->
    <transportConnectors>
      <transportConnector
uri="tcp://localhost:16163?jms.prefetchPolicy.queuePrefetch=1"
discoveryUri="multicast://myBrokerNetwork"/>
    </transportConnectors>   
<!-- config the store and forward model for broker network --> 
    <networkConnectors>
      <networkConnector uri="multicast://myBrokerNetwork"
                        name="bridge"
                        dynamicOnly="true"
                        networkTTL="10"
                        conduitSubscriptions="false"
                        decreaseNetworkConsumerPriority="false">
         <dynamicallyIncludedDestinations>
             <queue physicalName="myQueue"/>
         </dynamicallyIncludedDestinations>
      </networkConnector>  
    </networkConnectors>
    <!-- dispatch policy for load balancing -->
    <destinationPolicy>
      <policyMap>
        <policyEntries>
          <policyEntry>
            <destination>
                <queue physicalName="myQueue" />
            </destination>
            <dispatchPolicy>
                <roundRobinDispatchPolicy />
            </dispatchPolicy>
          </policyEntry>
        </policyEntries>
      </policyMap>
    </destinationPolicy>    
  </broker>
</beans>

what happened was:
when I run only Broker1 and Broker3 and Broker4, messages produced from
Broker1 got consumed well by consumers on Broker3 and Broker4.
when I add Broker2 to the above network, messages produced by Broker2 did
not get consumed at all. until I shut down Broker2, the messages queued
started to get consumed.

so my question is: why did this happen, is there a problem in my
configuration or might be a bug for activeMQ?
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