Re: Locking the BIOS?
Is the IDE/AHCI "swapping' you describe the only thing that's being changed within the BIOS when this happens?
Or is it, say, possibly changing a Serial Port or LPT Port that you have disabled and after this anomaly you find it/them changed too?
ie: Anything else in the BIOS that you may have changed from its Default setting, and afterwards find reset back to Default.
And pardon me, but for the price of a CMOS battery it isn't worth assuming it's good.
Even on new MB installs I replace them with a new known fresh one. Over there where our MB's are assembled, if there ever was a commodity item, button cells are certainly to be considered as one.
Mine: ASRock Z77 Extreme6, i7-3770K, 16GB Samsung MV-3V4G3D/US, SeaSonic X-750 Gold, On-die HD 4000, Corsair H80i, Antec Spot Cool, Fractal Design R4 Black Pearl w/Window
Hers: ASRock 990FX Extreme4, FX-8150, 32GB AMD/Patriot AE316G1601U2K, SeaSonic X-750 Gold, Asus HD7770-2GD5, Corsair H80i, Antec Spot Cool, Fractal Design R4 Black Pearl w/Window
Server: Gigabyte GA-990FXA-UD5, FX-4170, 32GB AMD/Patriot AE316G1601U2K, Enermax ELT500AWT, IBM ServeRAID M1015, Sapphire Ultimate HD 4670, Norco RPC-470