Error in genertated HTML

[dschwabe]

In every index, there is an extra, unmatched <th> element of class Index-header:

<table class=index_table>
  <th class=index_header>
    <thead>
      <tr>
        <th>Title</th>
      </tr>
    </thead>
    <tbody>
      <tr class=index_entry>
        <td class=index_entry_attribute>
          <a href="/navigation/context/o_19cd7e2e%401?p=o_DanielSchwabe_161c">Distance Learning</a>
        </td>
      </tr>
      <tr class=index_entry><td class=index_entry_attribute><a href="/navigation/context/o_19cd7e2e%402?p=o_DanielSchwabe_161c">Knowledge Management</a></td></tr>
      <tr class=index_entry><td class=index_entry_attribute><a href="/navigation/context/o_19cd7e2e%403?p=o_DanielSchwabe_161c">Adaptive Hypermedia Applications</a></td></tr>
      <tr class=index_entry><td class=index_entry_attribute><a href="/navigation/context/o_19cd7e2e%404?p=o_DanielSchwabe_161c">Semantic Web Applications</a></td></tr>
    </tbody>
  </table></span></div><div class=node_attribute><hr/><span ...