Java ExplicitDataListener stops listening

I am writing a Java program using the Java API (xbee-java-library-1.3.0.jar) that will connect a XBee2/3 to a SmartThings Hub. I have been following the packet layout listed in

I am running into an interesting problem. After sending several packets in the sequence I stop getting called by the ExplicitDataListener. I see in logging I am receiving the packet but even with a break point the callback never gets hit. This seems to be a timing related issue since it happens at different points of the sequence.

Example, I receive the packet (shown here in logging):
[Thread-1] DEBUG com.digi.xbee.api.DataReader - [COM6 - 9600/8/N/1/N] Packet received:
Packet: 7E001791286D97000206071B000001080000010411001E000100DA
Start delimiter: 7E
Length: 00 17 (23)
Frame type: 91 (Explicit RX Indicator)
64-bit source address: 28 6D 97 00 02 06 07 1B
16-bit source address: 00 00
Source endpoint: 01
Dest. endpoint: 08
Cluster ID: 00 00
Profile ID: 01 04
Receive options: 11
RF data: 00 1E 00 01 00
Checksum: DA

But the handler never gets called with the ExplicitXBeeMessage.

Here is the (incomplete) listener:
public synchronized void explicitDataReceived(ExplicitXBeeMessage explicitXBeeMessage) {
synchronized (this.myDevice) {
// this.myDevice.addExplicitDataListener(this);
final int clusterID = explicitXBeeMessage.getClusterID();
final int profileID = explicitXBeeMessage.getProfileID();
System.out.println("explicitDataReceived Profile " + profileID + ", Cluster " + clusterID);

		try {
			switch (profileID) {
			case 0x0000:
				switch (clusterID) {
				case ZigbeeMessage.ACTIVE_ENDPOINT_REQUEST:
					System.out.println("Received ACTIVE_ENDPOINT_REQUEST");
					ActiveEndpointsResponse.create(explicitXBeeMessage, (byte) 0x00, (byte) 0x01, (byte) 0x08)
					System.out.println("Received SIMPLE_DESCRIPTOR_REQUEST");
							.create(explicitXBeeMessage, (byte) 0x00, (byte) 0x08, 0x0104, 0x0002, (byte) 0x30)
					System.out.println("Undefined Profile " + profileID + ", Cluster " + clusterID);
				System.out.println("Undefined Profile " + profileID + ", Cluster " + clusterID);
		} catch (final Exception e) {
			// TODO Auto-generated catch block

One possibility I see is that the receiver runs on a thread pool. I have been using the Listener method to create and send response packets. Should I have a multi-thread Finite State Machine such that the listener simply records the event and then notifies the foreground thread to send the response? It’s a lot more work but I’m running out of ideas?

Note, the examples I’ve seen in the Java API are all very simplistic, sending only a few packets before exiting. It would be nice to have a full protocol engine there.

To answer my question, I modified my device handler to queue responses from the explicitDataReceived and send the responses in the foreground task and all appears to be working. Now on to handling the ZHA command requests.