Using the HTML header element safely

I'm clear that a site-wide banner should be marked up like this:

<header role="banner">...</header>

To prevent screen readers from announcing multiple banner landmark regions,
it seems like the only other safe use of a header element is inside an
article or section element. I am drawing this conclusion from my own
incomplete testing, and from reading these resolved bug reports:

https://bugs.webkit.org/show_bug.cgi?id=78992
https://bugzilla.mozilla.org/show_bug.cgi?id=849624

Does anybody have a test page or analysis, either to support or change my
conclusion?

Most of what I read on the Web either says to use a header element with the
ARIA banner role, or to use it with the full list of HTML5 sectioning
content elements (article, aside, nav, section) and sectioning root
elements (blockquote, body, fieldset, figure, td; and in the future,
dialog).

Would it be a good idea to file bugs against the browsers again, extending
the article and section element behavior to those other elements (other
than body)? I feel that authors who follow the HTML5 spec shouldn't
inadvertently send a bunch of banner landmarks to the AT.

-- 
Mitchell Evan
mtchllvn@gmail.com