Does HTML5 ban th cells from tbody?

I have the following markup as a part of a Razor view:

<table>
  <caption>Presidents</caption>
  <thead>
    <tr>
      <th scope="col">Name</th>
      <th scope="col">Born</th>
      <th scope="col">Died</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th scope="row">Washington</th>
      <td>1732</td>
      <td>1799</td>
    </tr>
    <!-- etc -->
  </tbody>
</table>

With the "target schema for validation" set to HTML5, Visual Studio complains thusly:

Warning 1 Validation (HTML5): Element 'th' must not be nested within element 'tbody tfoot'.

Is this really true? If so, could someone link to the spec?

My understanding was that using <th> for row headers was not just legal but encouraged. It certainly seems fairly common, I could link dozens of tutorials explaining (seemingly sensibly) that it helps with accessibility.

Is this a VS bug? A real change coming with HTML5 (a good one? a bad one?)? What's the story?