title: Delete file on mongoDb gridFs results in "0", even if it is there
body: <p>is there anything obvious I'm doing wrong with this code?</p>
  
  <pre><code>$result = $this-&gt;_grid-&gt;remove(
      $someQueryWithOneResult, array('safe' =&gt; true, 'justOne' =&gt; true)
  );
  if ($result['n'] === 0) {
      throw new FileNotFoundException("no file with xuuid '" . $xuuid . "'", 404);
  } else if ($result['n'] === 1) {
      return true;
  }
  </code></pre>
  
  <p>Sometimes the exception is thrown (meaning the result was 0). I'm quite sure the file exists and it is deleted afterwards. I run this in a batch job against a mongoDb cluster with 2 shards and 2 replicasets.</p>
  
  <p>I suspect a bug inside mongoDb either PHP driver (maybe 'safe' => true doens't work), or maybe some problem with the shard.</p>
  
  <p>Any ideas? Google couldn't really help :-(</p>
  
  <p>Regards</p>
  
  <p>Marko</p>