Странное поведение xml?

class Xml extends \DOMImplementation
{
	public function __construct()
	{
		$this->dom = $this->createDocument();
		$this->dom->encoding = 'utf-8';
		$this->dom->formatOutput = true;
		$this->dom->preserveWhiteSpace = false;
	}


	function addElement($node, $name, $text = '')
	{
		$element = $this->dom->createElement($name, $text);
		$node->appendChild($element);

		return $element;
	}


	public function getDocument()
	{
		return $this->dom->saveXML();
	}
}

$this->xml = new Xml();
$xmlMassage = $this->xml->addElement($this->xml->dom, 'Massage');

$xmlOrder = $this->xml->addElement($xmlMassage, 'Order');
$this->xml->addElement($xmlOrder, 'orderID', 416267);
...
return $this->xml->getDocument();