scrollTop() issue when returning to a scrolled page

scrollTop() issue when returning to a scrolled page

don't know if this is a browser bug...

I positioned a div at the bottom of the page just underneath the viewport, calculating it with $(document).height() and animate it to bottom:0, works great even when scrolling, cause of updating with the scroll-event.
but when I reload this page or scroll down a bit the original position value was used, so it animates to the original viewport value.

may I get a hint from the forum?
thank you in advance.
rolf