Playing in 16:9?

[iDarbert]

I don't know why, but even if the game does let me use 16:9 resolutions the game itself keeps working on a 4:3 aspect ratio, meaning that I see two vertical bars on the right and left side of the screen.
The game itself is running at 16:9 however, because I can move the cursor over the black bars, but nothing is rendered there except the army badges if I rotate the battlefield.

Anyone has a clue on what's going on? It's the Steam version and the demo used to take the whole screen, I also have a ATI graphics cards if that matters.