Originally Posted by
rudestuff
Because you've taken away the torque but you've still got a boot load of left pedal...
There it is in a nutshell. You've set the yaw trim (pedal displacement) to compensate for the torque, when you remove the torque you have to retrim the pedals or you will get a considerable left yaw. In a power off configuration the aircraft will actually require some right trim (from neutral) as the fuselage will have a tendency to rotate in the direction of rotation due to the friction reaction by the main gearbox.