title: Collection aggregator not aggregating response properly Mule ESB
body: <p>I have flow, where I will have multiple <code>Item</code> under the root Tag <code>Items</code>. I have splitter where it splits each items and doing some processing. After that I'm collecting all the response using Collection aggregator.</p>
  
  <p>In my flow, Observed collection aggregator waiting for something  though all the response are already reached aggregator. There is no response is being collected after aggregator ( since it is waiting for some response).
           But I'm sure ( if the Items has 5 item in it), all the response is being reach aggregator. But not sure why aggregator is still not passing its output(But sometime it is passing)</p>
  
  <p>If I have kept timeout 30000 in aggrgegator and failed on Timeout ="false", now it is been passed out and it is aggregating the response ( 5 items).</p>
  
  <p>But I'm pretty sure, message are reached aggregator within 20000 ms. But it is keep on waiting for something :(.</p>
  
  <p>Why this behaviour from collection aggregator. Do any one have clue?. Please find the config..</p>
  
  <pre><code>    &lt;flow name="Items" doc:name="Items"&gt;
      &lt;vm:inbound-endpoint exchange-pattern="one-way" path="QUEUE" connector-ref="VM_Q1" doc:name="QUEUE"&gt;
      &lt;/vm:inbound-endpoint&gt;
      &lt;splitter expression="#[xpath('/Items/Item')]" doc:name="Splitter"/&gt;
    &lt;vm:outbound-endpoint exchange-pattern="one-way" path="OUT1" connector-ref="MAIN_VM" doc:name="Test Queue"&gt;
   &lt;/flow&gt;
  
    &lt;flow name="Items1" doc:name="Items"&gt;
    &lt;vm:inbound-endpoint exchange-pattern="one-way" path="OUT1" connector-ref="MAIN_VM" doc:name="Test Queue"/&gt;
  .............doing some transformation and processing.....
  &lt;collection-aggregator failOnTimeout="true" doc:name="Collection Aggregator"/&gt;  
    &lt;/flow&gt;
  </code></pre>
  
  <p>Using version: 3.5.1
  How we can track what exactly it is wait?. I have kept logger and checked all the 5 items are populating before aggregator.
  Help will be more appreciated.Thanks.</p>
  
  <p>Edited:
   Logs after splitter component each iteration of Item</p>
  
  <pre><code>  After splitter:{MULE_CORRELATION_SEQUENCE=1, MULE_CORRELATION_GROUP_SIZE=5, MULE_ENCODING=UTF-8, MULE_CORRELATION_ID=9f7447b1-a03b-11e4-85dd-b8ee652d2686}
   After splitter:{MULE_CORRELATION_SEQUENCE=2, MULE_CORRELATION_GROUP_SIZE=5, MULE_ENCODING=UTF-8, MULE_CORRELATION_ID=9f7447b1-a03b-11e4-85dd-b8ee652d2686}
   After splitter:{MULE_CORRELATION_SEQUENCE=3, MULE_CORRELATION_GROUP_SIZE=5, MULE_ENCODING=UTF-8, MULE_CORRELATION_ID=9f7447b1-a03b-11e4-85dd-b8ee652d2686}
   After splitter:{MULE_CORRELATION_SEQUENCE=4, MULE_CORRELATION_GROUP_SIZE=5, MULE_ENCODING=UTF-8, MULE_CORRELATION_ID=9f7447b1-a03b-11e4-85dd-b8ee652d2686}
   After splitter:{MULE_CORRELATION_SEQUENCE=5, MULE_CORRELATION_GROUP_SIZE=5, MULE_ENCODING=UTF-8, MULE_CORRELATION_ID=9f7447b1-a03b-11e4-85dd-b8ee652d2686}
  </code></pre>
  
  <p>Log before collection aggregator</p>
  
  <pre><code>  Before Collection Aggregator:{MULE_CORRELATION_SEQUENCE=1, MULE_CORRELATION_GROUP_SIZE=5, MULE_ENCODING=UTF-8, MULE_CORRELATION_ID=13783281-a036-11e4-a356-b8ee652d2686, Content-Type=text/plain;charset=UTF-8}
    Before Collection Aggregator:{MULE_CORRELATION_SEQUENCE=2, MULE_CORRELATION_GROUP_SIZE=5, MULE_ENCODING=UTF-8, MULE_CORRELATION_ID=9f7447b1-a03b-11e4-85dd-b8ee652d2686, Content-Type=text/plain;charset=UTF-8}
    Before Collection Aggregator:{MULE_CORRELATION_SEQUENCE=2, MULE_CORRELATION_GROUP_SIZE=5, MULE_ENCODING=UTF-8, MULE_CORRELATION_ID=9f7447b1-a03b-11e4-85dd-b8ee652d2686, Content-Type=text/plain;charset=UTF-8}
    Before Collection Aggregator:{MULE_CORRELATION_SEQUENCE=2, MULE_CORRELATION_GROUP_SIZE=5, MULE_ENCODING=UTF-8, MULE_CORRELATION_ID=9f7447b1-a03b-11e4-85dd-b8ee652d2686, Content-Type=text/plain;charset=UTF-8}
   Before Collection Aggregator:{MULE_CORRELATION_SEQUENCE=2, MULE_CORRELATION_GROUP_SIZE=5, MULE_ENCODING=UTF-8, MULE_CORRELATION_ID=9f7447b1-a03b-11e4-85dd-b8ee652d2686, Content-Type=text/plain;charset=UTF-8} 
  </code></pre>
  
  <p>@David please suggest. MULE_CORRELATION_SEQUENCE=2 is repeating multiple times. But the fetching payload is correct and different for each correlation_seq=2. How can be this issue resolved?  </p>