Difference in ruling on same casebook play?

[just another ref]

This play is the opposite of the play where A is not awarded free throws and is awarded a throw-in. When discovered, if change of possession has occurred, and A has the ball again, now A gets both the free throws and the ball. In this case, the error is discovered while B has the ball, so B keeps the ball and A gets..........nothing.
Seems harsh when described this way, but if several possession had taken place since the error it seems less severe. For better or for worse, this is where the committee chose to draw the lines in this rule.