That's normal for i9100 ROMs on the i777. The i9100 only has two capacitive buttons, and one physical, so the map wrong on the i777.
Check out the i777 dev section, there is probably 10 ROMs by now, when you include CM7 and MIUI. Check out the hellraiser thread to port i9100 ROMs over. That may fix your issue, but I'm not sure, I don't know if it works after the fact.
Sent from my Galaxy S II (i777)
> HTC 8525
> iPhone 3G
> iPhone 3GS (it was a dark time in my life, I was confused)
> Palm Pre
> HTC Aria
> Samsung Captivate
> LG Thrill
> Samsung Focus
> Samsung Galaxy S II (I777)
> HTC One X
> Samsung Galaxy Note II (I317)
+ HP TouchPad