My 2011 FG FPV GS Falcon recently had a water pump replaced at 14,000 km. Ford replaced it with a modified water pump sent over from the US, and they also changed to a different coolant. Since then the thermo fan has been coming on flat-out quite regularly and sometimes for long periods of time, even when its only 14 degrees outside and I don't have air-con on! Ford couldn't find a problem with the fan and suggested that they have an active fan and that is quite normal. I told them that it didn't do it before the water pump got changed and they said well it should have!
It sounds as if the fan is coming on when it shouldn't, so have the dealer check the temperature when it does kick in, or simply have the fan replaced.