SUMO. are you using the rod setup or cables. you say if you push the cable back it frees up the brakes. these brakes were designed for rods with a big spring to pull it back when you release the peddle. to release the shoes from the drums
That is how I remember them, can't recall where the spring was fitted but it used to push the rods back. The brakes worked OK when fitted to the car so hopefully it isn't a huge problem. I have spare front drums and shoes if thats any help mate? not sure if they are the same though.