I have a Phenom II x4 960T, mine sometimes does this using my Asrock board.
If it set it to an overclock, say 4.0GHz usually the computer will turn off and reboot at 4.0. sometimes it doesn't reboot and just goes straight past the bios and it will be at the stock 3.0GHz with the same high voltage.
I found the best way with mine was after i set the overclock I turn off the computer, turn off the PSU then hold the power button for 10 Seconds. Then boot the computer in the normal way, check that it has taken effect in the bios then continue into the windows boot.
That works for me to keep my overclock, it may be worth a try for you to change your overclock slightly and see if this takes any effect.