Description:
------------
Copying an object doesn't appear to work as expected for either a shallow or a deep copy.  

Reproduce code:
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class Dummy {}

$listA = new Dummy();
$listA->next = new Dummy();
$listA->next->previous =& $listA;
$listA->value = "one";
$listA->next->value = "two";
$listA->next->previous->value = "ONE";
echo "ListA: ";
echo "(" . $listA->value . ", " . $listA->next->value . ") \n";

$listB = $listA;
$listB->value = "three";
$listB->next->value = "four";
$listB->next->previous->value="THREE";
echo "(modified listB)\n";
echo "ListA: ";
echo "(" . $listA->value . ", " . $listA->next->value . ") \n";
echo "ListB: ";
echo "(" . $listB->value . ", " . $listB->next->value . ") \n";

Expected result:
----------------
Expected output: (ie: if PHP does a deep copy)
    ListA: (ONE, two) 
    (modified listB)
    ListA: (ONE, two) 
    ListB: (three, four) 

This should happen because $listB->next->previous is a copy of the reference 
to $listA.  Modifying it should not modify ListA OR ListB.  

Possible (wrong) output: (if PHP had done a shallow copy)
    ListA: (ONE, two) 
    (modified listB)
    ListA: (THREE, four) 
    ListB: (three, four) 

This would be the case because listB's next would be a reference to ListA's 
next.


Actual result:
--------------
Actual output:
    ListA: (ONE, two) 
    (modified listB)
    ListA: (THREE, two) 
    ListB: (three, four) 

This looks like PHP did something between a shallow and a deep copy.
while ListB->next is a copy, ListB->next->previous still points at ListA. (!?!)

... For an added bonus, try replacing '= new' with '=& new' and it looks like
PHP does a shallow copy.  From my reading of PHP documentation, I thought PHP would always do deep (de-referencing) copies.