incorrect column count

HTML

<table id="colspan_test">
  <thead>
    <tr>
      <th>A</th>
      <th>B</th>
    </tr>
    <tr>
      <th colspan="2">Test</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>2</td>
      <td>3</td>
    </tr>
  </tbody>
</table>

JavaScript

$(document).ready(function() {
  $('#colspan_test').DataTable({});
});