Description:
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Strange object allocation issue, maybe related to PHP/LIBXML memory handling.

I've supposed that PHP releases the object associated to $root when I unset it (even if this object can be reached through $dom->documentElement).

Later, when I create the $ele element, it takes the same memory position of $root.


LIBXML version 2.7.8

Test script:
---------------
$dom = new \DOMDocument('1.0', 'UTF-8');
$root = $dom->createElement('root');
$dom->appendChild($root);

$h1 = spl_object_hash($root);
$h2 = spl_object_hash($dom->documentElement);

var_dump($root === $dom->documentElement); // true, OK
var_dump($h1 === $h2); // true, OK

unset($root);

$ele = $dom->createElement('ele');

$h3 = spl_object_hash($ele);
$h4 = spl_object_hash($dom->documentElement);

var_dump($h1 === $h3); // expected to be false, but actually true
var_dump($h1 === $h4); // expected to be true, but actually false


Expected result:
----------------
bool(true)
bool(true)
bool(false)
bool(true)

Actual result:
--------------
bool(true)
bool(true)
bool(true)
bool(false)