7850 and strange crash

Hi,

I've got Sapphire HD7850, stock clocks are 860 and memory 1200mhz. I OC it to 1200 core and 1400 memory, voltage about 1.175 - 1.2, rise cooler speed and temp never reach more than 80 degrees. BF3, DOTA 2 and LoL haven't crash it. There are no artifacts, color changes. And when I exit game and card's mode changes to idle then after few seconds, sometimes minutes I see green, blue or orange strips and my PC restarts. Color of the strips depends on clocks 1200 - green, 1100 - blue, 1050 - orange. I leave msi kombustor on all night, about 10 - 12 hours and nothing. On stock clocks this problem haven't occured. Have you got any idea?