"Barking" is caused by a pressure release (reverse airflow) through the compressor inlet. It happens when there is not enough exhaust energy to overcome the air pressure in the intake tract. When you lose the exhaust energy by taking fuel away, the compressor wheel turns into the shaft "driver" instead of being driven by the tubine wheel. It tries to drive the shaft in the opposite direction of normal rotation. Think of the weight of the turbine spinning over 60,000 rpm, and then try to change its direction of rotation in an instant.
If there were a vacuum in the intake tract, there would be no "bark". The wheels in the turbo would continue in thier normal direction and everything would be great. If you could come up with a way for that to happen, you would please many people. Until than, venting the pressure through a BOV instead of the compressor will have to do.

 

Thanks trendz, that makes more sense

Smokin has me thinking about routing the excess boost to the exhaust... that seems like it would be a great effect. you could also inturn have the pressure release valve double as a BOV with some sort of solenoid like soot4brains explained.