Description:
------------
I've been working on updating the referenced array while in loop, when I encountered an issue with array_merge - basically the code below will run indefinitely. If you'll change the `$value == 'a'` to `$value == 'b'` the code will successfully finish (the issue will occur for any non-last element of array); 

While array_merge doesn't solve my initial issue (as it seems to be working on array copy), I don't think such behavior is valid.

Test script:
---------------
<?php
 
   $array = array('a','b');
   $t = &$array;
 
   foreach($t as $value)
        if ($value == 'a')
            $t = array_merge($t, array('c'));
        else
            echo($value);
 
   var_dump($array);
 
?>

Expected result:
----------------
b

array
  0 => string 'a' (length=1)
  1 => string 'b' (length=1)
  2 => string 'c' (length=1)

Actual result:
--------------
Fatal error: Maximum execution time of 30 seconds exceeded