Here is a fix made by TeamBG.com to correct the flaw with Grand Mastery.

Here is what is said on there site:
"Attacks Per Round and Grand Mastery rules corrected to match BG/IWD/AD&D.
James Schumacher:
Grand Mastery is supposed to give you an extra attack, IT DOESN'T!!!!
They didn't even do the attacks per round to AD&D specs!!!!
I fixed this, I also fixed the bonus Thac0 and damage specs to that of BG and IWD.
Nobody messes with my GRAND MASTERY!!!!"

Here is the link, just scroll down to BG2. http://teambg.gnnetwork.com/downloads.html

Nice eye. I thought something was fishy. I have a couple of questions, though. What did you change regarding the thac0 and damage modifiers on weapons? Is it better or worse than the way they've got it now? And how in hell do I install the files????
Thanks,
oSo