[Plugin: Tweetbacks] Proper Syntax to Generate Results

From the implementation guide on Yoasts site, it says:

<?php if ( ! empty($comments_by_type['tweetback']) ) : ?>
  <h3 id="pings">Tweetbacks</h3>
  <ol class="commentlist">
  <?php wp_list_comments('type=tweetback'); ?>
  </ol>
<?php endif; ?>

If I do not have the if around the wp_list_comments area I see a tweetback result, however when it is inside this if statement I do not. I’ve tried several other alternatives but cannot get a filtered state to only show when tweetbacks exist.

Closest I got was trying to write wp_list_comments into a variable and if that was empty then display, but it does not have an option to echo as a variable and the callback function was giving me fits.

Suggestions appreciated.