On some airplanes flight idle comes on as soon as the aircraft is airborne, on others, like e.g. the jurassic, it comes on at a certain landingflap setting. On the jurassic the fan speed is above normal, low idle during flight at higher IAS. This, like a lower than one EPR, might be an indication of negative thrust.
Of course if you shutdown the engine completely the negative thrust will be even lower.