DOMXML module crashes on call remove_attribute() method for a node, which was previously created by for example set_attribute().
 Take a look at the following example:

<?php
$xml = xmldoc('<root a1="b1"/>');
$root = $xml->root();
$root->set_attribute('a2','b2');
$root->remove_attribute('a1');
$root->remove_attribute('a2');
echo htmlspecialchars($xml->dumpmem());
?>

Removing "a1" attribute is ok because it was defined in XML document on parse time. But removing of "a2" attribute causes PHP to crash.