ActiveMQConnection threads in parked state during startup

I've implemented a JMS producer using org.apache.activemq.ActiveMQConnectionFactory API. In the deployment they are 10 threads launched and each thread invokes the following sequence of methods which wrap around the ActiveMQConnection API.

connector = new ActiveMQConnect();
connector.setEndPointURL(primaryURL, secondaryURL, connectorQueryString);
connector.setCredentials(userName, password);
connector.initializeConnection();
connector.setDestinationQueue(queueName);
connector.addMessageToQueue(message);
connector.sendMessageToQueue();

The call to initializeConnection in turn invokes the following code which returns the connection

1) ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory(m_userName, m_password, m_endPointUrl);
2) m_queueConnection = connectionFactory.createConnection();
3) m_queueConnection.start();

However, (and potentially under load), a large % of the threads enter the parked state and stay there. The stack trace for these threads is as follows:

java.lang.Thread.State: WAITING
at sun.misc.Unsafe.park(Native Method)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:118)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1841)
at java.util.concurrent.ArrayBlockingQueue.take(ArrayBlockingQueue.java:341)
at org.apache.activemq.transport.FutureResponse.getResult(FutureResponse.java:40)
at org.apache.activemq.transport.ResponseCorrelator.request(ResponseCorrelator.java:80)
at org.apache.activemq.ActiveMQConnection.syncSendPacket(ActiveMQConnection.java:1195)
at org.apache.activemq.ActiveMQConnection.ensureConnectionInfoSent(ActiveMQConnection.java:1289)
at org.apache.activemq.ActiveMQConnection.start(ActiveMQConnection.java:456)
at ActiveMQConnect.initializeConnection(ActiveMQConnect.java:63)

The JMS producer connects using failover transport to an active/passive or primary/failover configuration.

Is the problem being caused by the failover URL? The documentation seemed to indicate that the failover URL can be sent with format:

failover:(tcp://amq01:61616,tcp://amq02:61616)?queryString....

Would appreciate any advice so I can resolve this issue.