I don’t see why the custom post type would affect the query orderby.
If the query is invalid (for example, wrong post type) WordPress would revert to a default query posts by date descending, so double-check the post type you’re using is valid.
You can also try this code (add it to a theme file) – it should show what posts WordPress is selecting without using MapPress at all:
<?php $wpq = new WP_Query('post_type=uk&orderby=date&order=desc'); print_r($wpq); ?>
Finally, try disabling your other plugins and switching to a standard theme for a moment. Some themes/plugins modify the WordPress query.