I have two custom widget areas defined in the Header area, working perfectly in 3.6.4. Updated to 3.6.7 and applied all fixes. Only one widget area showed up on the site - the second one. The first widget area still showed up in the Widgets admin page with the right contents, but updating and deleting contents of the area still didn't get it to show up on the site.

So I deleted the widget area completely and recreated it. Now it doesn't show up in the Widgets admin page at all, let alone on the site.

Reverting to 3.6.4 immediately made the widget area visible in both the Widgets admin page and on the live site.

Is there some problem in 3.6.7 in having two custom widget areas defined in the same area?

Have you applied all the bug fixes for 3.6.7 as outlined in New Versions and Updating?