Thanks for the heads up.
It's supposed to be a responsive theme, which means it tries to adapt to different resolutions. I think you just happen to have a weird one. If you resize your window to be smaller horizontally the sidebar should disappear completely, and place itself below the main content section. I guess it just overlaps a little bit before it gets to that, and you are right on the edge maybe.
There are a couple problems with formatting that need to be dealt with at some point when I have some free time, and I'll add that to the list.