blog site is distorted

I am at http://www.itaintthemustard.com and recently when I publish the site produces a distorted version of the theme by overlaying the right column onto the left column. This is the second time this has happened on this blog. After a week or so of no help, I simply changed the theme and the problem went away. But this time I’d like to figure out what is causing this to happen. Anyone got a clue?