Issues with prev_post and next_post helpers

[kevinansfield]

We've had a report of bugs with {{prev_post}} and {{next_post}} helpers:

 <aside class="read-next">
    {{#next_post}}
    <a class="read-next-story {{#if image}}" style="background-image: url({{image}}){{else}}no-cover{{/if}}" href="{{url}}">
        <section class="post">
            <h2>{{title}}</h2>
            <p>{{excerpt words="19"}}&hellip;</p>
        </section>
    </a>
    {{/next_post}}
    {{#prev_post}}
    <a class="read-next-story prev {{#if image}}" style="background-image: url({{image}}){{else}}no-cover{{/if}}" href="{{url}}">
        <section class="post">
            <h2>{{title}}</h2>
            <p>{{excerpt words="19"}}&hellip;</p>
        </section>
    </a>
    {{/prev_post}}
</aside>

the prev_post and the next_post does not works, it output the last article in any post by next_post, the prev_post output nothing.

@AileenCGN has also observed this behaviour but exact reproduction steps are currently missing.