IE Overlay Height

+1. This works for me, too.

It occurred in IE7.you can see this condition at attached img.

This fix doesn't well work when the document is very short. (In IE 7 at least.) This seems better:

        positionOverlay: function(){
            var dimensions = document.viewport.getDimensions();
            Control.Overlay.container.setStyle({
                width: Math.max(
                            document.body.clientWidth,
                            dimensions.width) + 'px',
                height: Math.max(document.body.clientHeight,
                            dimensions.height) + 'px'
            });
        }