post thumbnail isn't using resized images

[Denis-de-Bernardy]

it seems like the new post thumbnail feature neither crops images, nor uses thumbnail images when available.

get_the_post_thumbnail() and set_post_thumbnail_size() seem to use the size of post-thumbnail, but image_downsize() only seems to understand a size of thumbnail.

this results in huge images in posts, even when the size is small.

adding this code in a theme fixes the issue, in case anyone needs a temporary fix:

add_filter('image_downsize', 'my_thumbnail_downsize', 10, 3);
$thumbnail = get_the_post_thumbnail();
remove_filter('image_downsize', 'my_thumbnail_downsize', 10, 3);

...

function my_thumbnail_downsize($in, $id, $size) {
	if ( $in || $size != 'post-thumbnail' )
		return $in;
	return image_downsize($id, 'thumbnail');
}

I believe this was was fixed by [15002] Re-open if not, and provide a "did, expected, observed."