Ok if the front brakes are being operated out of the front reservoir, then almost everything I have said may be wrong.
Here's the deal
Inside your M/C are two pistons linked but operating independently.If you were to disconnect the line to the rear brakes, and then stomp the brakes, this is what goes on; The footpedal is connected to the pushrod, which is connected to the rearmost piston. the end. Pedal goes down, piston moves forward. On the front of the piston is a Mini pushrod. When the rear piston moves forward the mini pushrod eventually reaches the front piston. If you have enough pedal travel left, the front piston will push fluid out to the front calipers. if you still have pedal travel left the brakes will apply and the pressure will build, stopping the car.