function series_issue_manager_unpublish($series_ID, &$published, &$unpublished)
{
    // take the series out of the published list
    $key = array_search($series_ID, $published);
    if (FALSE !== $key) {
        array_splice($published, $key, 1);
        update_option('im_published_series', $published);
    }
    if (!in_array($series_ID, $unpublished)) {
        // add to the unpublished list
        $unpublished[] = $series_ID;
        sort($unpublished);
        update_option('im_unpublished_series', $unpublished);
        // change all published posts in the series to pending
        $posts = get_objects_in_term($series_ID, 'series');
        foreach ($posts as $post) {
            if (get_post_status($post) == 'draft') {
                continue;
            }
            wp_update_post(array('ID' => $post, 'post_status' => 'pending'));
            wp_set_post_series($post, $post, true, $series_ID);
        }
    }
}
function wp_set_post_series_draft_transition($post)
{
    remove_action('save_post', 'wp_set_post_series');
    $post_ID = $post->ID;
    $ser_id = wp_get_post_series($post_ID);
    wp_set_post_series($post_ID, $post, true, $ser_id, true);
}