You should end up at A-10 after penalizing team A half the distance for the FM foul from the basic spot, which is the end of the related run, as it is by the team not in possession. 1/10 team B.
You are not missing anything. The only way team A would get the ball is if team B declines the penalty for the FM foul (I can think of only one scenario where that would happen, and even then team A would not really benefit from getting the ball back).