Using categories with custom post types

[Bill Murray]

I have a custom post type named 'community', and I've registered it with taxonomies to include 'category'. I've also added:

PHP Code:

register_taxonomy_for_object_type('category', 'community'); 


immediately following the register_post_type() command. However, a link to the category archive to which the CPT's are assigned doesn't show the CPT's. Since I only have CPT's assigned to that category, I get the 'no posts match...' response to the query.

If I add a filter to the query with this code ...

PHP Code:

if ( !is_admin() ) {
    add_filter('pre_get_posts', 'query_post_type');
    function query_post_type($query) {
        if(is_category() || is_tag() || is_home() && empty( $query->query_vars['suppress_filters'] ) ) {
            $post_type = get_query_var('post_type');
            if($post_type)
                $post_type = $post_type;
            else
                $post_type = array('post','community','nav_menu_item');
        $query->set('post_type',$post_type);
        return $query;
        }
    }
} 


the CPT's show up in the category archive just fine.

Does anyone have any idea why the register_taxonomy_for_object_type() doesn't accomplish that, forcing me to add the filter? Until I got the function right, it was breaking nav menus, and the admin check was something that became necessary in WP 3.1. If I could avoid adding the filter, I'd really like to do that.