do_meta_boxes HOOK runs 3 times (how to stop it)

the do_meta_boxes HOOK runs 3 times in this file:
https://svn.automattic.com/wordpress/tags/3.5/wp-admin/edit-form-advanced.php

do_action('do_meta_boxes', $post_type, 'normal', $post);
do_action('do_meta_boxes', $post_type, 'advanced', $post);
do_action('do_meta_boxes', $post_type, 'side', $post);

This causes everything I do (like var_dumps) to be spit out 3 times.

What can I add to my function to only have it run for a certain context, like just “advanced”, and not the others?