jonkirkman

It seems like it only works if you make it the first value of the argument array.
Try:

register_post_type('foo', array(
	'hierarchical' => true,
        'labels' => array(
		'name' => 'Foo',
		'singular_name' => 'Foo'
	),
	'description' => 'A Foo',
	'public' => true,
	'supports' => array(
		'title', 'editor', 'author', 'page-attributes'
	),
	'show_ui' => true,
	'menu_position' => 20,
	'capability_type' => 'page'
));