Let's say we have a list (UL, OL — no matter), some list items and block element inside 'em. This block element have border-left and padding-bottom styles. As a result, in IE6 all following items will be shifted to left on the width of the left border of block element.
(Should be viewed in IE6).
Hint: click right button on the frame and view the source as HTML.
Solution consist in removing any of the bug conditions (border-left or padding-bottom) or in adding redundant border-bottom style with color of the background.