title: Siddhi Kafka source sometime produces two events for a single source event
body: <p>I'm testing pattern locally in Siddhi tooling 5.1.2 deployed to Docker.</p>
  
  <p>I've got Kafka topic with 7 events, which visible using other monitoring tools. I defined a source and store all events to rdbms. A query is very simple: <code>from my_stream select * insert into my_table;</code>
  By some reason, in DB I see 17 records which are actually 7 pairs of identical events. There is no special configuration, no errors.</p>
  
  <p>I've tried to <code>down &amp;&amp; up</code> docker-compose with the tooling, changed group-id of the source. Sometimes changing of group-id helps, but the problem comes back.</p>
  
  <p>I would expect only 7 events to be read and stored to DB.</p>
  
  <p>Why could it produce duplicated events?</p>