I've noticed that my website, which appears as intended on all desktop browsers I've tested, suffers from a puzzling background image positioning issue on iPhone, iPod touch, and iPad.

I've been working with this sample page:

Here is a screenshot on regular Safari:

Here is a screenshot from Mobile Safari on an iPad:

Here is the relevant portion of the stylesheet:
body {
	margin: 0;
	padding: 0;
	border: none;
	background-image: url(images/banner_bg_lite.png);
	background-position: top center;
	background-repeat: no-repeat;
	background-color: #FFF;
	background-attachment: scroll;
Any ideas? Site still functions, but this bug is totally breaking the visual style, and I can't seem to figure out what's causing it.