Amnesia The Dark Descent Demo problem

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I have a bit of an unusual problem. And I'm not sure if this is supposed to happen (I don't think it is).

The lighting and the particle effects are turned the right way up, but the textures (i.e., everything else) is upside down, as if it has been flipped horizontally. :/

I have tried reducing the graphics, and have updated the drivers (and yes, restarted). Still nothing.

Help?