I’m sure you’re already aware of this but IE is a pain in the butt. I just spent more time than I like to admit trying to figure out why my dropdown menu would not stay open (on mouse hover) over my stupid slideshow. At first I thought it was because my stupid slideshow had a z-index value that was too high. So I spent time messing that up. But then I noticed a very curious thing: when I added a background color to the ul, the menu stayed open over the slideshow.
I had added a background color to the ul but I’d used rgba for a transparent-ish background.Lower versions of IE(less than IE9) ignore rgba and I knew this. What I didn’t know, shockingly enough was that lower versions of IE will create a bug when they have an element with z-index and no background color. So if you want your drop down menus to stay open on hover over another element (no matter if it has z-index or not) you better add a background image or a color or both.
IE is so EVIL!!!!!!!!!!!!!!!!!