Description:
------------
I'd like to print the xml string in my code, so i use function asXML(). But it just return the element value in the xml. 

Is the code before i use asXML effort it?

Reproduce code:
---------------
<?php

..........
..........
..........//Here is some code. If there is no these codes,it will be OK.


$string = <<<XML
<a>
 <b>
  <c>text</c>
  <c>stuff</c>
 </b>
 <d>
  <c>code</c>
 </d>
</a>
XML;

$xml = new SimpleXMLElement($string);

echo $xml->asXML();
?> 

Expected result:
----------------
<?xml version="1.0" ?><a><b><c>text</c><c>stuff</c></b><d><c>code</c></d></a>

Actual result:
--------------
text stuff code