Description:
------------
When extending DOMDocument, it's class properties cannot be overwritten/changed. DOMDocument's initial value are kept.

var_dump() however contains the actual new value, so behaviour is buggy at least.

See http://3v4l.org/6H88X

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

class A extends DOMDocument 
{
    public $formatOutput = true;
}
$a = new A;

var_dump($a->formatOutput); // false
var_dump($a); // Has formatOutput => true

Expected result:
----------------
bool(true)
object(A)#1 (34) {
  ["formatOutput"]=>
  bool(true)
  <<cut>>
}

Actual result:
--------------
bool(false)
object(A)#1 (34) {
  ["formatOutput"]=>
  bool(true)
  <<cut>>
}