I bought ArmA 2 off Steam, but I have a custom launcher (Better mod management etc) for it now, but whenever I enter shift-tab mode on Steam it doesn't seem to stop switching buttons (Due to TAB key).
Now that may not seem like a big problem, but it is.

If the server owner does anything with the server (entering a menu, stopping the game, or something completely different doesn't even have to be the owner) you get stuck in the game, you can't move and you can't use your keyboard.
You can only use your mouse, this is very annoying mostly in LAN games.