"Next Post" link doesn't reflect re-ordered posts

Hello,

I’ve installed the plugin (it’s great, thank you!) and the reordering is working fine. However, in my project pages I have a “prev post” and “next post” navigation, these do not reflect the reordered posts. Can you advise me on what can be done to fix this please?

I am using the following code for the post navigation:

<span class="prev-arrow" title="Previous project">
   <?php next_post_link('%link', __('←')); ?>
</span>

<span class="next-arrow" title="Next project">
   <?php previous_post_link('%link', __('→')); ?>
</span>

http://wordpress.org/plugins/post-types-order/