title: array_walk throwing a warning; claims invalid callable
body: <p>Using PHP version 5.4.27, the following code throws a warning and fails.</p>
  
  <pre><code>$test = ['a', 'b', 'c'];
  array_walk($test, function (&amp;$value, $key) { $value = 1; });
  var_dump($test);
  </code></pre>
  
  <p>Result:</p>
  
  <blockquote>
    <p>Warning: array_walk() expects parameter 2 to be a valid callback, no array or string given in [snip]/test.php on line 3</p>
    
    <p>array(3) { [0]=> string(1) "a" [1]=> string(1) "b" [2]=> string(1) "c" }</p>
  </blockquote>
  
  <p>Any thoughts as to why this is happening?</p>
  
  <p>Resolved: This is actually due to eAccelerator not working correctly with anonymous functions. Switch to Zend Performance Suite or APC.</p>