I have a theory. I'm not sure how valid it is, but I'll share it. My P4 has exhibited this phenomena also. The air circulation of the craft is quite clever, and quite different than P3P. Air enters the belly of the craft using a fan, as we have all seen by now in photos. The air is pushed up through the craft, then out the motor pod vents. The air circulation through these vents is helped with suction created by the venturi of the propeller thrust racing downward over the top of the motor pod (I think that's so clever). When the rushing air is split by the motor pod arm, it's compressed slightly. As the air goes past the arm, it's uncompressed and speeds up, causing a venturi suction affect. This draft of the passing air helps by sucking air out of the motor arm bottom vents. My theory is the pressure differentials of this rushing air at different throttle levels is affecting the barometer sensor inside, causing the craft react with altitude changes, unpredictably. Turning left or right happens to amplify these pressure changes (negative or positive) because of the change in pressure from the craft spinning to turn. This could potentially change the venturi, and change in craft's interior barometric pressure, ever so slightly, affecting the accuracy of the barometer sensor readings. Again, it's just a theory.