Validator.nu: "Attribute role not allowed on element h2 at this point."

Why not?

I have this in an otherwise-valid HTML5 + SVG 1.1 + MathML 2.0 + RDFa
Lite 1.1 document:

<hgroup>
  <h1>Company Name</h1>
  <h2 role="presentation">Tagline</h2>
</hgroup>

Spec says:

> Authors must not set the ARIA role and aria-* attributes in a manner that conflicts with the
> semantics described in the following table, except that the presentation role may always be used.