1972 Chevy El Camino Bleeding brakes

I have replaced the master cylinder kit on my pickup. I then bled the wheels following the sequence, longest line first to closest last.

My problem is that the fluid from the front bleeding nipples only trickles out when its bled. The rear wheels however, shoots out rapidly when i bleed them.
Is this normal or an indication of some type of problem?
The entire bleeding process is done with the engine not off.

I would appreciate any help