I'm AA PLT as well and they wouldn't let me choose a seat for free. Even though it is supposed to be a benefit of One World Sapphire. This was in October, haven't flown an AA coded flight on IB since then. I got so frustrated calling both airlines about it, searching flyertalk for the answer i wanted, and eventually resigned to a standard coach seat. I wasn't pleased but I got over it. Just another reason for me to try and book BA metal on TATL trips.