If the front pads were replaced recently as you state, the rear brake pads could still be causing the light to come on. The application of the parking brake applies a different brake system than the normal service brakes. The parking brakes are a set of brake shoes (not pads) which utilize the center section of the rear rotors as it's drum.
I am not sure if your car has rear sensors though, they do vary a little from model to model.
It is fairly normal for the brake pad warning to flicker on and off, mostly coming on when the brake pedal is depressed.
Another possiblity is that when the front pads were replaced that the sensors were improperly installed.