Heading inside table cell is not supported

The following:

<table>
  <tr>
    <th> 
== heading 1 ==
    </th>
    <th>
== heading 2  == 
    </th>
    <th> 
== heading 3  == 
    </th> 
  </tr>
</table>

stop the table when hitting the first heading and then it get lost.

In MediaWiki this content properly produces headings inside table cells.

See https://bitbucket.org/axelclk/info.bliki.wiki/issues/41