Jeffrey Zeldman on fixing A List Apart for IE6:
MSIE6 has trouble calculating the heights of block level elements. Eddie Traversa discovered the browser was caching the values it calculated on one page of ALA and incorrectly applying those values to other pages of the site.
Put simply, if the content area on page A was 200px high, and the same area on page B was 400px high, IE6 might display only the first 200px when it loaded page B. The initial value got stuck in the browser’s cache. This is the reason that manually reloading (for instance, by hitting F11) “fixed” the bug on a page by page basis.