They wrote NVIDIA about it and got a reply that a fix for the problem will arrive later this month.
Late last month, a TR reader who calls himself Cybercat alerted us to what he said was an inexplicable problem affecting some GeForce 8800 cards, and particularly the GeForce 8800 GTS 320MB. According to Cybercat, the problem causes random slowdowns, often halving frame rates until the user alt-tabs out of the game and back in again. More interestingly, the problem doesn't appear to be tied to any particular hardware configuration, Windows version, or display setting. Users with all kinds of setups have been reporting problems, from the Nvidia and eVGA forums to the NVNews, Rage3D, and Guru of 3D forums.