After adding a

$this->addPrefixPath('Form_Element', 'Form/Element', 'ELEMENT');

in a form constructor my special element is fine but it does not find the standard form elements 'submit'. Putting trace code in the plugin loader it appears that Zend_Loader::isReadable is saying it found a submit.php in my path, but there isn't so it fails to include the path and find the class.

This feels like a php error.

Any Ideas?