O Ases e o Dasilva não validam tabelas, creio que está com bug. Nem a tabela no WACG 2.0 http://www.w3.org/TR/WCAG20-TECHS/H63.html é validada.

 <table border="1">
  <caption>Contact Information</caption>
  <tr>
    <td></td>
    <th scope="col">Name</th>
    <th scope="col">Phone#</th>
    <th scope="col">Fax#</th>
    <th scope="col">City</th>
  </tr><tr>
    <td>1.</td>
    <th scope="row">Joel Garner</th>
    <td>412-212-5421</td>
    <td>412-212-5400</td>
    <td>Pittsburgh</td>
  </tr><tr>
    <td>2.</td>
    <th scope="row">Clive Lloyd</th>
    <td>410-306-1420</td>
    <td>410-306-5400</td>
    <td>Baltimore</td>
  </tr><tr>
    <td>3.</td>
    <th scope="row">Gordon Greenidge</th>
    <td>281-564-6720</td>
    <td>281-511-6600</td>
    <td>Houston</td>
  </tr> 

</table>  

Autor: marcus federico