I have:

```
MqttAsyncClient mq;
   ...
   mq = new MqttAsyncClient(myServer1,"app1");
   mq.connect();
   ...
   //(1)
   //doing something with mq (pub/sub)
   ...
   mq.disconnect();
   mq.close();
   //(2)

```

Now I am using a Monitoring Console and I see:

* In (1), 3 Mqtt threads:
MQTT REC, MQTT SND and MQTT Call
* In (2), 2 Mqtt threads:
MQTT SND and MQTT Call
* After further seconds only 1 thread
MQTT CALL

The CALL thread will never be stopped. 
How come ?