This is actually by design.

>Here is the problem. When you untie someone who is trussed
>you untie ALL of the knots not just the truss.

Trussing them supercedes bind hands and bind legs (it actually strips those affects)

>If you have the truss tied it would make sense to me that you
>would have to work your way down the progression after you
>untied the truss.

Truss is so much more powerful than bind hands and bind legs and is harder to undo that it replaces both of them. In other words...once you truss them, their hands and legs are no longer individually bound.