When editing a post or a page on my WordPress.com site, mediaofbirmingham.com, the right margin is not flush with the right edge of the WYSIWYG window.
* It looks fine in preview and published modes.
* I'm using Coraline theme, but it's not a theme problem; I switched temporarily to the Twenty Twelve theme, and the problem was still there.
* Of all my WP.com blogs, this is the only one that has this problem.
* No custom CSS: The only paid feature on this site is domain mapping.
I suspect this is a bug, and not fixable on my end. But if anyone has an idea, please let me know.
The blog I need help with is mediaofbirmingham.com.