i've noticed similar issues, but only when trying to overclock (or on the weird events my card says its running at 56 Ghash/s lol)
personally i think it's a driver issue, even with latest drivers its still going like that...
Nvidia is just bad for mining really.
I read another post from a guy with a gtx 470. He said when he clicked stop mining, it would shut off his PC. This sounds exactly like what mine is doing, it just happens to recover versus shutting down.
Nvidia doesn't seem to be suited for mining, no...
I'm wondering if its even worth my trouble. the gtx 470 can get about 100MH/s, but if i have to reboot my PC every time i stop mining just to reset my GPU core clock... I can see this getting old REALLY fast.
So basically, if i lower the AGGRESSION of the miner, it won't crash my display driver, however it will reduce the core clock to 405mhz when i try to stop mining.
Any tips/comments/suggestions would be appreciated.