I've seen this on my DFI board a few times, and I've seen it on some friends' boards, as well.
I'm running a 1.5 GH Athlon O/C'd to 2 GHz, and occasionally, my system wakes up and recognizes the CPU at it's default setting. It has happened most often after a system lock up or when I've temporarily added a piece of hardware, for example, when I plug in an extra hard drive or a different vid card.
Completely powering down and rebooting usually solves it, but there have been times where I've had to go into the CMOS and manually reset it. That has also worked for most of the other machines I've worked on.
There have been times where the new hardware was causing the conflict. For example, if the jumper on the hard drive was set incorrectly, or the motherboard didn't correctly recognize the "Cable Select" setting for a drive or my system just didn't like the particular vid card. In those cases, removing the new hardware resolved the problem, either on reboot or after resetting the CMOS.