title: Elapsed Filter Plugin weird behaviour
body: <p>I am using elapsed filter plugin for calculating time difference between multiple start/end events for a particular id.</p>
  
  <pre><code>if [StepName] == "Step1" and [StepStatus] == "start" {
      mutate { add_tag =&gt; "Step1_start" }
  } else if [StepName] == "Step1" and [StepStatus] == "end" {
      mutate { add_tag =&gt; "Step1_end" }
  } else if [StepName] == "Step2" and [StepStatus] == "start" {
      mutate { add_tag =&gt; "Step2_start" }
  } else if [StepName] == "Step2" and [StepStatus] == "end" {
      mutate { add_tag =&gt; "Step2_end" }
  } else if [StepName] == "Step3" and [StepStatus] == "start" {
      mutate { add_tag =&gt; "Step3_start" }
  } else if [StepName] == "Step3" and [StepStatus] == "end" {
      mutate { add_tag =&gt; "Step3_end" }
  } 
  
  elapsed{
      start_tag =&gt; "Step1_start"
      end_tag =&gt; "Step1_end"
      unique_id_field =&gt; "FrtId"
      new_event_on_match =&gt; false
      timeout =&gt; 1800
  }
  elapsed{
      start_tag =&gt; "Step2_start"
      end_tag =&gt; "Step2_end"
      unique_id_field =&gt; "FudtId"
      new_event_on_match =&gt; false
      timeout =&gt; 1800
  }
  elapsed{
      start_tag =&gt; "Step3_start"
      end_tag =&gt; "Step3_end"
      unique_id_field =&gt; "FudtId"
      new_event_on_match =&gt; false
      timeout =&gt; 1800
  }
  </code></pre>
  
  <p>The problem I am facing is, In-spite of the data being absolutely correct. For many documents I am getting "elapsed_end_without_start" tag. However for the same document I am having the start tag already present before in the file from which I am loading it. </p>
  
  <p>Any help will be appreciated. Thanks for A2A.</p>