In court testimony it came out that the tail on the Caravan produces positive lift with the flaps up. It produces downforce with take off flaps, 20 degrees. So when removing t/o flaps tail force is switching from down to up. If the flaps come up at too low an airspeed, the wing can interfere with airflow over the tail at the point when the needed tail force is switching from down to up. The plane pitches up, the wings stall, and you have an accident.