[Plugin: WP E-Cards] ft_wpecards_flush_rewrite_rules breaks register_post_type rewrite rules

Among other correction on the plugin, I replaced these two functions: ft_wpecards_flush_rewrite_rules() and ft_wpecards_viewcard_rewrite_rules( $wp_rewrite ) by:

function ft_wpecards_viewcard_rewrite_rules( $wp_rewrite ) {
global $wp_rewrite;
$new_rules = array( 'viewcard/(.*)' => 'index.php?ft_wpecards_view=1&card='.$wp_rewrite->preg_index(1) );
$wp_rewrite = $new_rules + $wp_rewrite;
return $wp_rewrite;
}
add_filter('rewrite_rules_array','ft_wpecards_viewcard_rewrite_rules');

http://wordpress.org/extend/plugins/wp-ecards/