When scrolling this site, if you scroll the page and then scroll the iframe on the right, only the smileys get repainted. Also, the clipping region seems off: if you only scroll the main page a little from the original position, and then scroll the iframe, the "clipping area" didn't seem to move.
This happens whether the patches in Bug #16339 and Bug #17946 are applied or not.
The link is dead and repainting logic has changed completely since 2008. I've never seen a bug like this. I'm going to close the issue, but feel free to reopen it if you find a similar problem elsewhere.