Okay. So boost blows into the crank. Gotcha.
The factory set up is the intake connected to the PCV. How is this instance not happening naturally then? (please excuse my ignorance. LOL)
The factory setup is,
1. PCV (Positive Crankcase Ventilation) = OEM setup is PCV (Valve) is connected to the intake manifold. If the car is under boost, then the PCV will close, if pressure pre-PCV is greater than intake manifold pressure or if you are off boost essentially in vacuum the PCV will open and dump into the intake manifold. By adding the OCC in between it will catch whatever waste that is being released by the PCV before going into the intake manifold. Because there is pressure/boost in this system, it is important the OCC and connections are completely sealed so that no boost is lost.
2. Vent/Breather = OEM setup is connecting the vent to the driver intake pipe going to the turbo. The vent is just to relief any pressure build-up and to supply the crankcase with air so that if the PCV releases air the vent/breather will supply clean air in its place, sometimes oil will come out if their is excess pressure or even excess oil due to overfill etc. This vent should not see any pressure/boost, the way it is connected from the factory is in the intake pipe before the turbo so in fact it is getting vacuum assist when the turbo sucks air.
With the dual setup, if both the PCV and breather/vent are connected in the same system and then you get pressure, the PCV will be closed and it will be directed to the breather/vent hence the problem.