It resets itself to stock speed? or does the multiplier simply go to a lower value?
If speed step, EIST or C1E is enabled, they can, while idle, make it look like you are at a lesser speed. Its a power saving function.
You can check for them in the Bios.
Just run some stuff when it steps down the speed, and if it instantly jumps back to OC mode, then that is what it is!
--Lupi