This problem exists in both IE6 and IE7. There are two identical DIVs, one after another, which have "position: relative" set. Inside the first one is another DIV with "position: absolute", which means it can be positioned relative to its containing div. It also has "z-index:1000", meaning it should display above any element that is either lacking an explicit z-index value or has a z-index value less than 1000. In most browsers (Firefox 1.5, Safari 1.3, Opera 8.5), this works as expeced. In IE6/IE7, the DIV is still drawn behind the second "base" DIV, which is incorrect.
This bug looks to be finally fixed in IE8 Beta 1