On Mediawiki: Preview is displaying both the preview and the editing box. This makes the "Keep editing" button a baffling concept, because you can keep editing where you are. We should hide the editing box again.
PS. I know that Quiddity and Hhhippo have suggested that we actually show both the preview and the editing box -- it's not a bad idea, and we can talk about adding that later, maybe with a "Refresh the preview" button. But breaking something and then moving stuff around the breakage isn't a great development plan. :) Let's fix the bug and then talk about the change.