iOS 5 has brought a number of nice things to JavaScript/Web Apps. One of them is improved scrolling. If you add
-webkit-overflow-scroll:touch;
It was frustrating to discover a known problem with stopPropagation and native div scrolling. It does not seem to prevent the onTouchMove from bubbling up, so that when scrolling beyond the bounds of the div (upwards at the top or downwards at the bottom), the entire page will bounce.
More discussion here and here.