Description:
------------
When setting reference to $this object, using "=&" operator in a class method doesn't seem to work as expected (or my understanding is completely wrong). When unsetting object outside of the class methods - link breaks and won't unset the referenced objects.

Reproduce code:
---------------
<?php 
class uu 
{ 
    public $ref; 

    public function set_me_as_ref(uu &$whom) 
    { 
        $whom->ref = &$this; 
    } 
} 

$obj1 = new uu(); 
$obj2 = new uu(); 

$obj2->set_me_as_ref($obj1); 

$obj2 = null; // this won't unset $obj1->ref, but unsets only $obj2 object 
// $obj1->ref = null; // this won't unset the $obj2 object, but unsets only $obj1->ref 

echo '<pre>'; 
var_dump($obj1, $obj2); 
?> 

Expected result:
----------------
$obj1->ref is supposed to be null
$obje2 - is supposed to be null

Actual result:
--------------
$obj1->ref => living object
$obj2 => null