Users with new role created with add_role don't appear in author meta box

Hi folks,

I’ve created a new role, let’s call it “Posters”. I’ve assigned this role three capabilities, the same three as a contributor gets:
– read
– edit_posts
– delete_posts

Users with this new role don’t appear in the author meta box.

From what I can tell, the author meta box uses wp_dropdown_users to generate the list, and it passes 'who' => 'authors'

This is then picked up, eventually, by WP_User_Query->prepare_query() which does this:

if ( 'authors' == $qv['who'] && $blog_id ) {
	$qv['meta_key'] = $wpdb->get_blog_prefix( $blog_id ) . 'user_level';
	$qv['meta_value'] = '_wp_zero_value'; // Hack to pass '0'
	$qv['meta_compare'] = '!=';
	$qv['blog_id'] = $blog_id = 0; // Prevent extra meta query
}

I don’t know the exact ins and outs but am I right in saying that this still uses user levels to generate the list, and it only gives users who have a user level greater than zero?

My assumption here is that users in a role created with add_role don’t have a user level, and are therefore not included by this query.

This seems odd. I’d even class it as a bug! This list should contain any user with the edit_posts capability, not any user with a non-zero user level.

Can anyone confirm that my understanding is correct? And if so should I log it as a bug? Also, is there a quick-and-easy way to get, say, users with the edit_posts capability included in this list?

It would also be nice to have some filter hooks in post_author_meta_box() and wp_dropdown_users() to allow some modification of the parameters used to build the query. The only way to edit this list from a theme/plugin seems to be to edit the HTML output of wp_dropdown_users using the wp_dropdown_users filter. Not ideal! Anyone agree?

Thanks