datepicker positioning/rendering detection does not work properly if DP is inside a fixed div located at bottom of page and the page is long

im trying to put a date picket inside a fixed div at the bottom of the page (facebook style mini nav).

ex:

<div style='position:fixed; bottom: 0'>
Date: <input type="text" id="datepicker">
</div>

if my page is short, the date picker is rendered above the field and inside the view port. but if the page is long the date picker is rendered outside the viewport and cant even be seen or partially seen. i think this has something to do with how the offsets are detected/computed. here is a sample of the full page which i edited from the demo to recreate the bug. try the date picker while you are on top of the page then try it when you scroll down let say at least in the middle of the page.