If the problem goes away when you cycle power to the receiver, it's not likely a transmitter problem, but something in the airborne system. If it's a transmitter problem, you should see it happen when you are using other airborne systems with different receivers and different servos.

If it happens with other receivers and servos, then you can safely conclude that the problem's in the transmitter. If it happens rarely, then even a trip to the service center may not find it...intermittent problems can be the devil to find and correct.