Description:
------------
The function "array_walk" ignores to pass the reference and passes the content instead for the parameter "userdata" if the "&" isn't written inside the "array_walk()" but inside the function definition ("function somename(&$value, &$key, &$userdata)"). This doesn't work for the "userdata"-parameter but it does work for the "value" and the "key"-parameter.

Have a look at the code at the bottom and the expected and the actual result. Now compare what would happen if you would call "my_function" manually by using

my_function($any_value, $any_key, $my_variable);
echo $my_variable;

and then using

my_function($any_value, $any_key, &$my_variable);
echo $my_variable;

In both cases $my_variable would be increased, of course.

So in my oppinion the userdata-problem it's not just inconsistency. It's a bug because a part of the function definition is beeing ignored.

Reproduce code:
---------------
<?
function my_function(&$value, &$key, &$userdata){
	$userdata++;
}

$my_array = array('one', 'two', 'three');
$my_variable = 1;

array_walk($my_array, 'my_function', $my_variable);
echo $my_variable;

echo '<p><hr></p>';

array_walk($my_array, 'my_function', &$my_variable);
echo $my_variable;
?>

Expected result:
----------------
expected output:

4
-----------
4

Actual result:
--------------
actual output:

1
-----------
4