With a custom tune, possibly. Basically what everyone is saying in different ways is that the ECU has a "preset" amount of air that it assumes is going back into the Intake from the BPV. As the MAF is BEFORE the BPV, this has to be the case. When you vent your excess boost pressure to the atmosphere (via BOV), you are fux0ring your intake and motor out of the air that the ECU is assuming is there.
BOV's are bad... UNLESS you have the supporting tuning for the ECU to adjust for all of the changes you are making to the car.
BOV's are NOT PnP on Subies