EDIT: I was an idiot. I simply had an image that was vertically long, so it "moved", because the scroll bars showed up. I know... :O

I'm having a lot of trouble figuring out why an image is moving the entire body, and it is a huge issue. You can check it out here: <http://needstackhelp.tumblr.com/>

So basically, if you click the "hide post" on the top right, it contracts the div, thus hiding the image. You will also notice whenever you click hide post, then show, it moves the entire body left and right slightly. Why so?
If I remove the image that reads "This is an image", however, the body stays in one place!

How can I fix this issue? I plan to always have an image inside the div, so it's a pretty important issue to me.

Also, for those who are going to diagnose the source, I'm sorry, I never thought anyone else would ever need to see the code, and I've just been a very lazy designer. Just use Chrome/Firefox's inspect element for the most part.