Description:
------------
I encountered an error while assigning multiple class to an object into another class.

Suppose to have a class A in which is defined a property. At the begin, I use the property as an instance of another class B, then I do an 'unset' of property before creating assigning it an instance of class C.

Reproduce code:
---------------
class B {
    # do something
}

class C {
    # do something
}

class A {
    private $_prop;

    function __construct() {
        $this->_prop = new B();
    }

    function Re () {
        unset($this->_prop);
        $this->_prop = new C();
    }
}

$h = new A()
$h->Re();
unset($h);

Expected result:
----------------
I expect it to work correctly (I read a post before where staff said it has been fixed in version 5.2.x).

Actual result:
--------------
it crashes when calling 'Re' method giving me an error:

Allowed memory size of ... bytes exhausted etc.