I have recently upgraded to Windows 8 and since then, I've been having some strange problems with the "tab" button on my keyboard in New Vegas. It doesn't regularly respond when I hit it, unless I hold down "shift" at the same time, which also brings up the Steam overlay. Practically speaking, this makes it almost impossible to check my Pip Boy using the default key-mapping I'm used to. If I try to assign something to "tab" in the remapping menu, it will work only if I hold down the key for a few seconds.

Especially frustrating is the fact that performing a clean install does not seem to work; the issue remains even after the game is installed fresh.

I do not have similar problems when playing Fallout 3 or Skyrim or when using any other program so it must be something to do with New Vegas. What's going on here?