Probably that. If the humidity is very high and it has rained, the pads stick with the rotors (it's actually the corrosion which is formed just between them. You might get the impression that the car won't start, even if you press the accelerator pedal, here a "thung" and then it will release. Take an...ear(!) when breaking afterwards: does the rear discs create an "abrasive" sound? If yes, then it's the corrosion still attached to the rotors. It will go away after 5-10 times of applying the brakes.