The sidebar & content area jumps down when you scroll down past the top navbar

Hello.

I installed your theme for the website Hollis TV & Appliance. Everything works great but I noticed that the sidebar on the left, and the content portion both jump downward about 100px once you scroll down past the navbar – then it remains static again. It looks like a code glitch and seems choppy, so I want to correct it as soon as possible.

I have seen other sites using what appear to be this theme (including the theme’s download page), without the same issue. Either they found it in the css or its a new issue?

Anyway I haven’t made any changes to the CSS or anything yet. I wanted to see if it was maybe a simple known error first.

Please advise.