Get some more up to date figures. http://www.w3counter.com/globalstats.php
Anyway yes I know IE has considerable market share. This is because it can force market share, not because it is particularly good in any way.
The software we use (SMF 1.1.x) was released when IE7 was the latest version. There have been considerable changes (some of them even for the better) in IE8 so glitches are possible. Note that if Microsoft had released their browsers with W3 standards support like every other browser has had for years then there would be no problem, so it's easy to see who is at fault here.
As I mentioned though I did used to run Firefox 2 and had no problems with it, and since Cheetah is seeing the same problem you are seeing it may not be browser-specific and it may be impossible to reproduce for testing. I'll look into it over the next day or two.
Devious, treacherous, murderous, neanderthal, sub-human of the West.