I looked at your site with
Firebug, and it looks like there's at least 1 extra closing div somewhere, but I'm not sure where. It's likely that the problem is in your content somewhere, as the demo uses the right column in multiple places without any issues; the fact that you've said you're having the same problem when testing on another theme is also a strong indication that it's content related.
I recommend checking the HTML of your page content to make sure you don't have any extra "</div>"s anywhere.