The plugin determines the width and height of the viewport on page load, but it’s using $(window).height() which looks at the size of the viewport and then absolutely positions the content div over the image, relative to the viewport/window.
Because the page isn’t loading at the top of the document, the content is absolutely positioned incorrectly, and at that point, there’s no way to get it back down. (The scroll bar issue is bizarre, but I guess just a side effect.)
The plugin needs to check scrollPosition somehow, and adjust the dimensions accordingly. I’m still thinking about exactly how that would work…
OK Smock and I just talked. Try changing the #bg div from position: absolute; to position: fixed; and see if that solves your problem. You might lose iPad functionality at that point, FYI, but it should fix the weird anchor problem. Then it’s your call how to handle it.
Also, we both suggest: maybe don’t use this plugin if you can help it cause it’s a nightmare of positioning hassles that will never stop tormenting you. 😀