[Sparky]

This is a bit of a head-scratcher. I don't have a definite answer, but lets think it through.

As you probably know, there are grooves cut into the conical part of the adjuster that prevent it from backing out under the spring pressure from the brake shoe assembly. Was a new adjuster installed with the new backer plate? If not, was the old adjuster inspected? Did you observe the normal "click" action when the brakes were first adjusted?

The other strange thing is that you say the brakes were too tight, but the adjuster was backed out all the way. Normally this would cause the brakes to be looser, not tighter. Did you notice the shoes dragging when you removed the drum?

Edit: I see Don said something similar when I was typing.