Slow Enemy Territory framerate and solution

This last weekend, I played Enemy Territory - Quake Wars with a friend of mine. First we played it at his place last week when I bought the game. There it ran fast. Then during the week I tried to play it at home, did the online update (500+ MB), and it ran slow. Initially I thougth it was the patch that gave problems. It was not the firewall (Panda), my ADSL internet connectino or Punkbuster which I had installed. Punkbuster did bring some portscan warnings on the firewall of my friend.

On Saturday, my friend and myself played the game at another friends place in a three player game and it ran fast. The next day (Sunday), I tried it at home and it was terribly slow. After trying to replicate all conditions present at the places of both of my friends, it came down to the fact that I have a second screen at home.

Solution: Unplug the second screen and reboot, or set up screen cloning, then Enemy Territory runs fast. The game seems to to think it has a really wide screen or something similar and even runs slow in 800x600 in low detail. I can actually run it on 1280x960 in high detail on my PC.