Description:
------------
I'm trying to include all the xi:include tags in a file but PHP seems 
to just ignore some of them. 

I'm using XML's that are known to work 100%. You can see the XML 
files here:
http://postbooks.svn.sourceforge.net/viewvc/postbooks/xtupledocs/trun
k/referenceguide.tar.gz?view=tar

Basically the problematic file is products.xml which is included from 
referenceguide.xml and contains more includes. They all get ignored.

Reproduce code:
---------------
...
echo "Importing XML document...\n";
	$document = new DOMDocument();
	$document->load( DOCBOOK_PATH );
	
	echo "Parsing <xi:include> tags...\n";
	xinclude_all( $document );
...

	function xinclude_all( &$document ){
		$counter = 0;

		$xpath = new DOMXPath($document);
		$xpath->registerNamespace('xi', $ns = 'http://www.w3.org/2001/XInclude');
		$includes = $xpath->query( "//xi:include" );
		
		while($includes->length){			
			$counter++;
			echo "Parsing <xi:include> layer number $counter. {$includes->length} <xi:include> tags on this layer. ";
			$document->xinclude();
			$includes = $xpath->query( "//xi:include" );
			echo "{$includes->length} includes to process on next layer\n";
		}
		
		echo "$counter <xi:include> tag levels parsed.\n";
	}


Expected result:
----------------
I expect all the includes to be parsed and included.

Actual result:
--------------
Only the 12 includes in the main referenceguide.xml file get 
included, then it just says that there is no need to further include 
as if there were 0 more includes in the DOM tree.
But the included data isn't there.