Yeah, the z-index IE bug, have you heard of it? I was bitten by it a couple of days ago. In my case, I had a list of text fields in a form layed out from top to bottom. The problem is, I have these interactive drop downs on that can activate just under the text fields when you focus on the field and there is a validation error, which I use relative/absolute positioning to get in the right place, and so the position: relative declaration triggers the IE bug which causes the text field beneath the one that has the focus to occlude its drop down. My solution? I now have a javascript snippet that runs as the dom is ready that sets the z-index of all the containers(the one that has position: relative) of the text fields in descending order. So for example, if you have 10 text fields, the first one would have its z-index: 10 and the last one would have z-index: 1.
In a related note, if you use the relative/absolute positioning technique, the child element that has position:
absolute is considered the child of the parent element that has position: relative in terms of z-index, which if you then have overflow: hidden on the parent element or its ancestors, the child element would get cut out if it's position is out of bounds, vs if you didn't have position: relative set on the parent element then the child would not get cut out because it's considered to be the child of the root element in terms of z-index.