OffsetTop calculation problems in IE8. The solution

http://support.microsoft.com/kb/976948/

"Important Do not install update 976749 if you have not installed cumulative security update 974455. If you install update 976749 without first installing cumulative security update 974455, Internet Explorer may not work correctly. If this occurs, uninstall update 976749, install cumulative security update 974455, and then reinstall update 976749."

Simple.