I got a very awkward and specific issue with a simplexml evaluation.
The code:
$simplexml = simplexml_load_string($xmlstring); var_dump($simplexml); var_
Have a look here: http://www.php.net/manual/en/language.types.boolean.php#language.types.boolean.casting
It says that SimpleXML objects created from empty tags evaluate to false. Maybe that's what's going on?