title: array_key_exists is not working
body: <p>array_key_exists is not working for large multidimensional array. For ex </p>
  
  <pre><code>$arr = array(
      '1' =&gt; 10,
      '2' =&gt; array(
          '21' =&gt; 21,
          '22' =&gt; 22,
          '23' =&gt; array(
              'test' =&gt; 100,
              '231' =&gt; 231
          ),
      ),
      '3' =&gt; 30,
      '4' =&gt; 40
  );
  </code></pre>
  
  <p>array_key_exists('test',$arr) returns 'false' but it works with some simple arrays.</p>