Tactics Trainer error

Dark_N_Stormy_Knight

I'm playing "http://www.chess.com/tactics/server.html?id=88865&practice". After the correct first move Qf1, white should play KxN but moves instead to b3 and cuts my rating.  Something wrong here.  

nyLsel

If Kxd3 then ...Ba6# The computer moves only postpones the inevitable checkmate. 

Dark_N_Stormy_Knight

Thanks, I've got it now.