Confused by Bios Flashing (Restrictions)

[sponge_bob_128]

Searched around a bit but couldn't find an answer. The short of it question is how does ASUS cause utilities like AFUDOS to fail (verify fail) flashing a BIOS? BIOS ROM holes? Unflashable (hardware) regions?

Longer story: Wanted to downgrade a ASUS Sabertooth P67 UEFI Bios from just released latest version to just previous version 3209 --> 2302. For some bizarre reason ASUS does not allow this with their tools. I tried EZFlash, AIUpdate (and read BUPDATER also refuses)). So question #1: Why does ASUS restrict this???

Enraged, of course I tried to force the issue, following some instructions on the net that use AMI AFUWIN and then AISuite in sequence. The AMI tool complained that it could not verify the BIOS. The machine booted but the BIOS (2302) seemed to run in a restricted state, multipliers were locked and BIOS options were missing. Is this because it is running the "CrashFree" BIOS repair mode (Q#2)?

I then tried to flash back to 3209 and the motherboard was bricked.

Got a replacement BIOS from ebay (also have official ASUS one coming) and for some reason they sent me two (for different motherboard versions?), one that worked another that didn't. So I got to play with the spare ebay BIOS. I successfully hot-flashed (via AFUDOS) the spare BIOS chip with the old (2302) BIOS version file and it verified and worked great.

The question comes up when I tried to flash the original (bricked) ASUS BIOS using the same technique and AFUDOS complained and then did not verify. So question #3 is why is this? Are the chips (ASUS original vs EBAY) different? How does ASUS restrict flashing the BIOS (with AFUDOS)?? The verify error comes when I specify that the "non critical region"/ ROM hole #0 (/K0) to be flashed. The resulting BIOS is just like above, running in a restricted mode.

Since, my machine works fine, this mostly a "why is this/how do they do that?" questions.