如何防止fancybox-2后面的页面滚动

We are using fancybox2 for displaying images. Everything works well, but when the larger image is displayed in the fancybox, the page behind scrolls to the top. After closing the fancybox the user has to scroll back downwards to the position, where he opened the box. The examples on the fancybox2 Site do not show this behaviour. I could not find out, where is the difference to make this happen. We are using fancybox2 for displaying images. E