Lightbox in IE 7.0

I am using the Lightbox JS v2.03.3 Plugin when people click a picture.

Also I’ve added a filter to my header.php.
This way I don’t have to add the “rel” everytime I write a post.

The problem is in IE (not in FireFox), when I scroll down the page, and then click an image. The black halftransparent background stays at the top of the page.
It seems as if Firefox loads the lightbox background for the whole page, but IE just loads it for the first viewable section of the page.

Does anyone understand what I mean? Please help if you do.