title: Facebook PHP SDK, when calling Graph API with 'privacy' => custom unexpected behavior?
body: <p>I am trying to post something to my own feed via facebook's php SDK with privacy => custom. The message appears on my feed just fine, it also indicates the users I had selected just fine. But the users I had selected are not able to see the post.</p>
  
  <p>Here's what I am working with:</p>
  
  <pre><code>    try {
          $privacy = array(
              'value'     =&gt; 'CUSTOM',
              'allow'     =&gt; $users_string
          );
          $statusUpdate = $this-&gt;facebook-&gt;api('/me/feed', 'post', array('message'=&gt; $content, 'privacy'=&gt; json_encode($privacy)));
          return "true";
      } catch (FacebookApiException $e) {
          return json_encode($e-&gt;getMessage());
      }
  </code></pre>
  
  <p>As mentioned, I can see the post come up in my feed, and I can see what users are allowed to view the post. But when I view my own wall as one of those users, the post doesn't show up.</p>
  
  <p>I think I have narrowed down the problem to somehow incorrect $users_string. It's basically json object that I receive and transform into a string using this code: </p>
  
  <pre><code>    $users_string;
      for ($i=0; $i &lt; count($users); $i++) 
      { 
          if($i == 0)
          {
              $users_string = $users[$i];
          }
          else
          {
              $users_string = $users_string . ", " . $users[$i];
          }
      }
  </code></pre>