I really don’t know what would make those post types unique.
I have several times seen conflicts with other plugins and themes that affected queries. They can really difficult to troubleshoot, so I still think it’s always worth disabling plguins and switching the theme as a first step.
You can also try just taking MapPress out this – try just running the query and printing the results instead.
For example in yout template page do this instead of do_shortcode() :
$wpq = new WP_Query("posts_per_page=-1&post_type=projects");