1. It could be a booster going out. Keep an eye on it and see if it gets worse.
2. The stronger pressures could have popped the wheel cylinder. I think it was just because you panic stopped it and that caused it. Replace both rear wheel cylinders.
3. You missed a step in the bleeding process. It goes as follows.
RR, RL, FR, FL
Open a front bleeder and press the pedal all the way to the floor.
Re-bleed the rear brakes starting with the RR. Close the front bleeder and re-bleed
RR,RL,FR,FL