Description:
------------
If we try to change the array elements in one foreach loop using referenced 
$value, and in a second foreach loop remove some elements from the array, then 
the resulting array misses some element, some elements are duplicated, or simply 
nothing is removed, depending on that, which element we want to remove from the 
array in the second loop.

Test script:
---------------
$a=array(array('a'=>'11', 'aa'=>'22'), array('a'=>'33', 'aa'=>'44'), array('a'=>'55', 'aa'=>'66'));
foreach ($a as &$v) // if we use $k=>$v here
{
	$v['c']='99'; // and $a[$k]['c']='99' here, then it produces the expected result
}
foreach ($a as $k=>$v)
{
	if ($v['aa']=='22')
	{
		unset($a[$k]); // 
	}
}
print_r($a);


Expected result:
----------------
Array
(
    [1] => Array
        (
            [a] => 33
            [aa] => 44
            [c] => 99
        )

    [2] => Array
        (
            [a] => 33
            [aa] => 44
            [c] => 99
        )

)

Actual result:
--------------
Array
(
    [1] => Array
        (
            [a] => 33
            [aa] => 44
            [c] => 99
        )

    [2] => Array
        (
            [a] => 55
            [aa] => 66
            [c] => 99
        )

)