I’m sorry, but I don’t know what that plugin does. One thing that might help: you can try running the query in your template, without MapPress. That might help to determine if the role plugin is modifying the query somehow.
Here’s a snippet of PHP that’ll show a query (you can replace it with the query from your mashup):
<?php $wpq = new WP_Query('post_type=post&posts_per_page=-1'); echo print_r($wpq, true); ?>