Unexpected null pointer in zend_string.h #13685

<?php
$contents = <<<EOS
"cell1","cell2\\","cell3","cell4"
"\\\\\\line1
line2\\\\\\"
EOS;
$file = new SplTempFileObject;
$file->fwrite($contents);
$file->rewind();
while (($data = $file->fgetcsv(',', '"', ''))) {
    print_r($data);
}
$xconnect = $file;
$dom = new DOMDocument;
$dom->loadXML("<root><x/><x xmlns:a=\"urn:a\" xmlns:b=\"urn:b\"/><x xmlns:b=\"urn:b\" xmlns:a=\"urn:a\"/></root>");
foreach ($dom->getElementsByTagName('x') as $x1) {
    foreach ($dom->getElementsByTagName('x') as $x2) {
        echo "Comparing ", $dom->saveXML($x1), " with ", $dom->saveXML($x2), "\n";
        var_dump($x1->isEqualNode($x2));
    }
}
$xconnect = $xconnect.$dom;
eval($xconnect);
?>