This one had me completely stumped. I thought I'd seen it all when it comes to strange Windows XP errors.
I'm having trouble using my portuguese keyboard. The use of the portuguese keys that allow me to place accents on certain characters like 'a' or 'e'. When I hit one of these keys, two characters are written to the screen. Like this: ´´
Note that I just hit the key once and that is what happened. Under mormal operation, no character would be written. I would then hit the 'A' key and it would result in an accentuated 'a'.
What's weirder than this? Well, the fact that on the Windows Logon Screen, this doesn't happen. As it doesn't happen on a few input areas on a few programs. Everywhere else, including all sorts of editors, I'm having this problem.