Impression cylinder out of balancing

Hi i'm aware this is offset printing page while i using a flexo printing machine. My machine is water cooled impression cylinder. When machine is off, the impression cylinder i can rotate by using hand freely. However, it always return to a specific position while other printing unit does not have such symptom.Can give me some idea how can this happen? Is like the centroid of the cylinder no longer lies along the shaft so it always return to a specific position.