Close Site Menu Div Tag Error

Hi guys.

I found a strange error in the site menu code that I can't quite track down.

The code generated is:

<div id="site-menu" class="grid-12">
<div>
<ul class="links main-menu">
<li class="menu-237 first">
</li>
<li class="menu-229 last">
</li>
</ul>
</div>
<div/>

Note the last end div call. This leads to heaps of issues.

I've gone through the page.tpl.php file, and the close site menu div tag is correct:

<?php if ($main_menu_links || $secondary_menu_links): ?>
        <div id="site-menu" class="grid-<?php print $header_menu_width; ?>">
          <div><?php print $main_menu_links; ?></div>
          <div><?php print $secondary_menu_links; ?></div>
        </div><!-- /#site-menu -->
      <?php endif; ?>

Any idea what the cause is?