天佑的自由天地

This version fixed the bug of duplicated posts that appeared in a scenario that

echo $related_posts;

is placed in a separate template and use

$theme->display( 'foo' );

to display that template.

The problem was caused by plugin hook 'action_add_template_vars()' called several times and output is always appended to template variable '$related_posts' due to no initialization is done.

Thanks Brando and miklb for reporting this problem. You can grab the updated version from the original post.