In the Zend_Db_Table_Row_Abstract->findParentRow method it tries to include the $parentClass by directly calling Zend_Loader::loadClass($parentTable). I would expect it to use My_Loader as I set it with Zend_Loader::registerAutoload('My_Loader'). If we're adding stuff to the __autoload stack, we should be using it. I would propose wrapping it in a if(!class_exists($parentClass,true)) which will autoload it based on the __autoload stack as expected. Im Zend_Loader::loadClass() is being called all over the place without first checking the __autoload stack.