Custom Post Type Pagination

I am using custom post type that is hierarchical.

I have no trouble excluding children from the query by using:
parent=0

This exclusion, however, doesn’t apply to the next_posts_link and previous_posts_link. I want to navigate using only the parent.

Here is my code:

<?php $showposts = new WP_Query('post_type=events&post_parent=0'); while($showposts->have_posts()) : $showposts->the_post(); ?>
<?php the_title( '<h2><a href="' . get_permalink() . '" title="' . the_title_attribute( 'echo=0' ) . '" rel="bookmark">', '</a></h2>' ); ?>
<div>
  <?php the_content(); ?>
  <p><?php next_post_link('%link', '« Newer Issue' ) ?></p>
  <p><?php previous_post_link('%link', 'Older Issue »') ?></>
</div>
<?php endwhile; ?>