Description:
------------
When registering a new base node type with registerNodeClass: if I re-use variable names for created elements, then custom properties revert to their default value.

Test script:
---------------
<?php

class myDOMElement extends DOMElement
{
    public $myProp = 'Some default';
}

$doc = new DOMDocument();
$doc->registerNodeClass('DOMElement', 'myDOMElement');

$node = $doc->createElement('a');
$node->myProp = 'A';
$doc->appendChild($node);

# This seems to alter node A in $doc, not what I expected:
$node = $doc->createElement('b');
$node->myProp = 'B';
$doc->appendChild($node);

# Note: $nodeC instead of $node, this works fine. 
$nodeC = $doc->createElement('c');
$nodeC->myProp = 'C';
$doc->appendChild($nodeC);

foreach ($doc->childNodes as $n) {
    echo 'Tag ', $n->tagName, ' myProp:', PHP_EOL;
    var_dump($n->myProp);
}

Expected result:
----------------
Tag a myProp:
string(1) "A"
Tag b myProp:
string(1) "B"
Tag c myProp:
string(1) "C"

Actual result:
--------------
Tag a myProp:
string(12) "Some default"
Tag b myProp:
string(1) "B"
Tag c myProp:
string(1) "C"