Aftermarket BOV's have a higher spring rate than factory bov's. So where the factory bov will open up when releasing light throttle, the aftermarket one does not. Please correct me if i'm wrong. when there is no bov this causes a build-up of pressure in the intake piping, slowing the compressor wheel - and hence the flutter. I think the same principle applies to aftermarket BOV's which don't open under light load, but obviously you don't have as much of a pressure build up as you would jumping off the gas from WOT.
There are a few war-threads where everyone has thrown their 2c in about BOVs which might be worth a read such as this.