Does anyone know the actual answer for this? I've been experiencing this problem with ie 8 and 7. Finally got fixed in 9 i guess? Haven't tested in anything earlier than those. I found a few articles and threads that said to make the position relative or declare a height. Lots of other weird things. But i found that using the "background" shorthand was my issue (which one person said this was irrelevant). I noticed using the dev tools that none of the style for the background image were being applied so I wrote each of them out on their own and now it works fine.
I also forgot to mention the offending code that caused this in the first place which was from here http://www.cssstickyfooter.com/. Not only did it cause my footer background to disappear but also 2 other elements using the background shorthand.