Why is the sidebar wrapping under the blog posts only on home page?

Hello all,

I am confused about what is causing the side bar to wrap under the blog posts on the homepage of this site. It just started doing this.

http://soobahkdo.com/

The sidebar behaves correctly on the blog page:

http://soobahkdo.com/blog/

The side bar also behaves correctly on a blog post with a sidebar:

http://soobahkdo.com/bullying-awareness-guidebook/

On the home page when any pagination link is clicked, then the sidebar behaves correctly on those pages.

Is this a CSS issue or is it something else at play here?

Any insights appreciated.

Thanks!