title: DynamoDB ConditionalCheckFailedException thrown but succeeds
body: <p>I think that have seen in many occasions that a DynamoDB conditional put throws ConditionalCheckFailedException but succeeds. Usually in this scenario, the request takes quite long (~10s) to finish, but I can see that the request is updated despite the fact that a ConditionalCheckFailedException is thrown (and the it took few seconds).</p>
  
  <p>By the way I don't force any timeout on the DDB request.</p>
  
  <p>Is this a bug, or some DDB conditional put contract that I misunderstand? Has anyone experienced this issue?</p>