possible bug in register_post_type() in handling of 'supports' arg

I’ve discovered what I think is a bug in register_post_type(). I’ve searched the forums and tickets and haven’t found anything about this issue. I wanted to ask about it here before opening a ticket to make sure I’m correct.

Suppose I call:

register_post_type ('test', array ('supports' = array ('title', 'revisions'))) ;
$supports = array_keys (get_all_post_type_supports ('test')) ;
// $supports is now array ('title', 'revisions'), as it should be

After that, suppose I call:

// re-register post type with additional supported features
register_post_type ('test', array ('supports' => array ('title', 'editor', 'revisions'))) ;
$supports = array_keys (get_all_post_type_supports ('test')) ;
// $supports is now array ('title', 'editor', 'revisions'), as it should be

After that, suppose I call:

// re-register post type with fewer supported features
register_post_type ('test', array ('supports' => array ('title', 'editor'))) ;
$supports = array_keys (get_all_post_type_supports ('test')) ;
// $supports is now array ('title', 'editor', 'revisions'), but should be array ('title', 'editor')

That is, if I re-register a post type with more supported features, those extra features are there. However, if I re-register a post type with fewer supported features, the larger list of features is still there.

Digging into the core source for register_post_type() at line 1277, I see

if ( ! empty($args->supports) ) {
		add_post_type_support($post_type, $args->supports);
		unset($args->supports);
	} elseif ( false !== $args->supports ) {
		// Add default features
		add_post_type_support($post_type, array('title', 'editor'));
	}

and at line 1578, I see:

function add_post_type_support( $post_type, $feature ) {
	global $_wp_post_type_features;

	$features = (array) $feature;
	foreach ($features as $feature) {
		if ( func_num_args() == 2 )
			$_wp_post_type_features[$post_type][$feature] = true;
		else
			$_wp_post_type_features[$post_type][$feature] = array_slice( func_get_args(), 2 );
	}
}

Since add_post_type_support() just (as it’s name implies) adds to whatever features are already there, shouldn’t register_post_type() remove any existing supported features before calling add_post_type_support()?

That is, shouldn’t there be something similar to the following added before line 1278?

global $_wp_post_type_features ;
if (isset ($_wp_post_type_features[$post_type])) {
	$_wp_post_type_features[$post_type] = array () ;
	}

Note: I’m not suggesting this is the best fix (I’m not that familiar with the core code), but it seems to produce the correct behavior.