AMQ4.1.1: External broker drops transport connector for unknown reason

[um...@comcast.net]

I have two peers A.xxx.com and B.xxx.com connected using external brokers running on each.
A and B each have a number of applications that have transport connections to the
respective brokers.

    [clients] <--- tcpConnector ---> [ext Broker A] <=== NetworkConnector ===> <extBroker B] <--- tcpConn --> {clients]

The brokers startup fine and the clients connect respectively as shown in this log:

      2008-04-17 10:23:53,097 [127.0.0.1:41762] DEBUG TransportConnection            - Setting up new connection:    
                    org.apache.activemq.broker.TransportConnection@1f04ea6
     2008-04-17 10:23:53,098 [127.0.0.1:41762] DEBUG AbstractRegion                 - Adding consumer: 
                   ID:A.xxx.com-41697-1208452947300-1:9:-1:1
     2008-04-17 10:23:53,140 [127.0.0.1:41762] DEBUG AbstractRegion                 - Adding destination: 
                   topic://ActiveMQ.Advisory.Producer.Topic.com.xxx.topic.configuration_change

But as soon as a client on A publishes a message on a topic (com.xxx.topic.configuration_change),
broker A seems to remove the transport connection to the client as follows:


     2008-04-17 10:23:53,188 [127.0.0.1:41762] DEBUG AbstractRegion                 - Removing consumer:                  
                   ID:A.xxx.com-41697-1208452947300-1:9:-1:1
     2008-04-17 10:23:53,190 [127.0.0.1:41762] DEBUG TransportConnection            - Stopping connection:    
                  /127.0.0.1:41762
     2008-04-17 10:23:53,190 [127.0.0.1:41762] DEBUG TransportConnection            - Stopped connection: 
                  /127.0.0.1:41762

Why does this occur? What would be the recommended way to troubleshoot this problem?
Any hints appreciated...

Regards

/U