let me ask you something say if you restart dose it keep the overclock or dose it restart again with default clocks -if this is the case it means your OC isn't stable and it is setting your OC back to stock untill you get it stable and once you have it stable it won't do that ..
My gigabyte P45 board did that when i had unstable oc's -but the good news is you won't have to re-input all your values in the bios as once you re-enter the bios all the values will be where you left them . My advice add voltage seems like it isn't stable somewhere but apart from that i don't have enough info to advise you any further.
E8400 @ 4.2ghz idle 30c load 50-53c 3x 640gb
4850 mobo gigabyte P45 -UD3P @525 fsb g.skill PI ddr2 1066/ AMD 64 4200x2 @ 3.1ghz 24/7 stable MSNSLI -Deluxe
