I had this problem with my A65, also with a steel backing plate, after installing new brake shoes. What it boiled down to was that the anchor strap did not have the correct bend in it and it was pulling the backing plate (or the brake shoe pivot) one way or the other. I had the anchor strap on and off for re-bending four or five times before I got it exactly right. It must lie absolutely flat and parallel against both the backing plate (with big washer) and the passenger peg lug, such that the strap is not pulled in either direction as it's tightened down.
I guess there was enough slop in the old brake shoes that it wasn't a problem. Also, I've found that the new brake shoes swell. First time out, when I thought I had the brake adjusted right, after a few miles on the road the brakes got hot and started dragging. I found I had to back off the adjuster more than where it was set with the old brake shoes.