XML file with XIncludes: with example1.xml the second XInclude is not resolved properly. When changing the order as in example2.xml all XIncludes are resolved properly.

example1.xml

<?xml version="1.0" encoding="utf-8"?>
<parts>

  <part name="content">
    <h1>XML xinclude example</h1>

    <div>
      <h2>some some blog entry</h2>
      <p>blog entry comment</p>
      <p>2011-10-12</p>
    </div>

    <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="" xpointer="xpointer(/parts/part[@name='comments']/node())"></xi:include>
  </part>
  
  <part name="comments">
    <h2>Comments</h2>
    <form action="index" method="post">
      <ul>
        <li class="clearfix">
          <div class="left"><label for="AddComment_mail"><xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="" xpointer="xpointer(/parts/part[@name='label_AddComment_mail']/node())"></xi:include>:*</label></div>
          <div class="right"><input type="text" name="AddComment_mail" id="AddComment_mail" size="30"></input>
                 <input type="hidden" value="1" name="AddComment_entryId"/>
          </div>
        </li>
        <li class="clearfix">
          <div class="left"><label for="AddComment_content"><xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="" xpointer="xpointer(/parts/part[@name='label_AddComment_content']/node())">
		  </xi:include>:*</label></div>
          <div class="right"><textarea name="AddComment_content" id="AddComment_content" rows="5"></textarea></div>
        </li>
        <li class="clearfix">
          <div class="left"/>
          <div class="right"><input class="btn_submit" type="submit" value="Submit" name="AddComment_submit"/></div>
        </li>
      </ul>
    </form>
  </part>

  <part name="label_AddComment_mail">
      Mail
  </part>
  
  <part name="label_AddComment_content">
      Comment
  </part>
  
</parts>

example2.xml

<?xml version="1.0" encoding="utf-8"?>
<parts>

  <part name="comments">
    <h2>Comments</h2>
    <form action="index" method="post">
      <ul>
        <li class="clearfix">
          <div class="left"><label for="AddComment_mail"><xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="" xpointer="xpointer(/parts/part[@name='label_AddComment_mail']/node())"></xi:include>:*</label></div>
          <div class="right"><input type="text" name="AddComment_mail" id="AddComment_mail" size="30"></input>
                 <input type="hidden" value="1" name="AddComment_entryId"/>
          </div>
        </li>
        <li class="clearfix">
          <div class="left"><label for="AddComment_content"><xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="" xpointer="xpointer(/parts/part[@name='label_AddComment_content']/node())">
		  </xi:include>:*</label></div>
          <div class="right"><textarea name="AddComment_content" id="AddComment_content" rows="5"></textarea></div>
        </li>
        <li class="clearfix">
          <div class="left"/>
          <div class="right"><input class="btn_submit" type="submit" value="Submit" name="AddComment_submit"/></div>
        </li>
      </ul>
    </form>
  </part>

  <part name="label_AddComment_mail">
      Mail
  </part>
  
  <part name="label_AddComment_content">
      Comment
  </part>
  
  <part name="content">
    <h1>XML xinclude example</h1>

    <div>
      <h2>some some blog entry</h2>
      <p>blog entry comment</p>
      <p>2011-10-12</p>
    </div>

    <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="" xpointer="xpointer(/parts/part[@name='comments']/node())"></xi:include>
  </part>
  
</parts>

libxml_xinclude.php

<?php
$doc = new DOMDocument();
$doc->load('example1.xml');
$doc->xinclude();
echo $doc->saveXML();
echo "===========================================\n";
$doc = new DOMDocument();
$doc->load('example2.xml');
$doc->xinclude();
echo $doc->saveXML();
?>