I have seen this many times. Just played a hand and my GIB partner threw a trick, deliberately. Dummy was east of me and my partner had the King of trumps with 2 others. Having reached 5 tricks (ops bid 2H so were one trick from being set) my partner lead his king of trumps which of course got taken by west with the ace. There was absolutely no need to do that. The king was safe. Fortunately we still set the ops but we should have set by 2 not 1 trick. As I say, I have seen this done many times before. Are GIBS programmed not to get over tricks or to set by more than is required? Thank you