In IE9 the cart dropdown list is not displayed correctly, see attached image. Only the border is displayed but not the content.
Any information is welcome.
I can see the drop down in IE9 on my pc but I am on Windows 7 so that may be the difference.
Works fine for me too in IE9 on Windows XP and Windows 7 on the demo store and all my customised sites. From your screenshot, it looks to be most likely a CSS issue.