brake bleeding..WTF?

'Course that doesnt explain how the fronts are suppose to work at all if the rear lines blows said
the pedal side of the piston compresses a spring, (in the absence of hydraulic pressure in the rear reservoir/system), till it bottoms on the second piston, and compresses the fluid in the front system,.. thus the pedal seems to "go to the floor",, but actually just travels till it reaches the second system... cheers