I have a problem with IE9 on the group 'add/remove users' screen. When first loaded, the selection boxes look as expected:
After typing into either of the 'search' boxes, the panels change as shown here (the background seems to switch to 'transparent'):
The entries are still there, but white-on-white ... this doesn't seem to happen on FireFox
I've tried tracking down the CSS that causes this without success.