UI.DatePicker is positioned incorrectly in a scrolling div

I have a field with UI.DatePicker attached inside a scrolling div, and when you scroll down in the DIV, the popup shows in the wrong place. I made the following change - it seems to work for me in IE7, FF2, Opera, but I do not know if there will be any side effects or problems in other browsers.

	/* Find an object's position on the screen. */
	_findPos: function(obj) {
		while (obj && (obj.type == 'hidden' || obj.nodeType != 1)) {
			obj = obj.nextSibling;
		}
		// START HACK -DJM
		var pos = $(obj).offset();
		return [pos.left, pos.top];
		// END HACK -DJM
		// -SNIP-
	}

The HTML is something like this:

<div style="overflow: auto; height: 200px">
<br /><br /><br /><br /><br />
<input name="date" />
<br /><br /><br /><br /><br />
</div>