DOM XML module handle XML namespaces in a wrong way. Take a look at a simple example:

<?php
$xml = xmldoc('<?xml version="1.0"?><root xmlns:m="http://www.m.com/"/>');
$root = $xml->root();
$child = $root->add_child($xml->create_element('m:child'));
echo 'Namespace prefix: '.$child->prefix().'<br>';
echo 'Node name: '.$child->tagname().'<br>';
?>

It is obvious, that result should be:
Namespace prefix: m
Node name: child

But instead we have:
Namespace prefix:
Node name: m:child

 Moreover, it is even possible to create nodes with undeclared namespaces, like:

$child = $root->add_child($xml->create_element('q:child'));

and it will not return any errors. But XML document itself will be invalid after it, because of undeclared namespace.