This isn't a bug. You didn't actually play a game, as the opponent forfeited, so you get some minutes (43 in this case if you set Starter, Backup and Reserve as the same player) but you don't get full training minutes. This is because it shouldn't be so easy to get training if the other team forfeits.
If you have 3 different players for starter, backup and reserve then you will get the full 48 minutes spread between them in a forfeit.