KeyboardDevice[Key key] is not reporting absolute key state:

I have only tested this on Windows 7 64 bit.

The issue can be reproduced using a GameWindow, and in the constructor, attaching to the KeyDown event. In the handler, check if the KeyboardKeyEventArgs.Key == Key.Enter. Also check whether Alt is pressed. To check the alt key, do this:

this.Keyboard[Key.AltLeft] || this.Keyboard[Key.AltRight]

If both conditions are met (alt + enter), change the fullscreen state or something obvious.

This works, but the alt key has to be released and depressed for this boolean expression to equal true again.