With IE6 (again) and explorer theme 2.4 the right scrollbar sometimes disappears. I (mostly) can reproduce it with a page, where a image (example) is bigger than the width of the browser window - -- RalfGroß 2008-11-05 10:01:46
browser window width bigger than frame content: 
browser window width smaller than frame content: 
workaround is refreshing the IE6 window with F5.