Absolutely-positioned children of a relatively-positioned table will be positioned relative to the window, not the table.
A relatively positioned table with an absolutely positioned element placed inside of it will not calculate the correct position – relative to it’s parent – but instead render the absolutely-positioned element in relation to the browser window itself. This does not reproduce when the same absolutely-positioned element is placed inside other relatively-positioned elements such as DIVs, however. Best suggestion, should this be an issue for your design, is to avoid the case entirely.
This issue originally documented by Peter-Paul Koch at quirksmode.org (Read original article).