After upgrading to 2.7, the visual editor displays my themes header image in the content box. And when I enter my post or page content, the header image expands with the content. My header image is mostly black, so I can't see anything as I type. Of course I can see my text ok in the html editor, but I like to be able to switch back and forth.
This is very frustrating, and I have no clue how to fix it.