So it was disc brake front all along with both masters?
My guess would be the front discs have too much runout causing them to push the pistons back into the callipers. When you apply the brakes the first time all it does is push the pistons back but there is not enough fluid to push them all the way to the disc, which means another application is necessary.
Do you feel a pulsation through either the car or pedal when braking?
Solution is to machine your rotors.