Description:
------------
Only old-style call pass by reference works with array_merge_recursive, but the 'new' way doesn't

Reproduce code:
---------------
<?php
  $ar     = array('a'=>array(1,5,9,12=>array(1,3,5,200)), 1,3,100, 100=>array(1,9,50));
  
  //--- ONE ------------------------------------
  $result_one = array();
  array_walk_recursive($ar, 'walker_one', $result_one);
  function walker_one($v, $k, &$result)
  {
    $result[ $v ] = $v;
  }
  
  //--- TWO ------------------------------------
  $result_two = array();
  array_walk_recursive($ar, 'walker_two', &$result_two);
  function walker_two($v, $k, $result)
  {
    $result[ $v ] = $v;
  }
  
  var_dump($result_one, $result_two);

Expected result:
----------------
array(7) {
  [1]=>
  int(1)
  [5]=>
  int(5)
  [9]=>
  int(9)
  [3]=>
  int(3)
  [200]=>
  int(200)
  [100]=>
  int(100)
  [50]=>
  int(50)
}
array(7) {
  [1]=>
  int(1)
  [5]=>
  int(5)
  [9]=>
  int(9)
  [3]=>
  int(3)
  [200]=>
  int(200)
  [100]=>
  int(100)
  [50]=>
  int(50)
}

Actual result:
--------------
array(0) {
}
array(7) {
  [1]=>
  int(1)
  [5]=>
  int(5)
  [9]=>
  int(9)
  [3]=>
  int(3)
  [200]=>
  int(200)
  [100]=>
  int(100)
  [50]=>
  int(50)
}