I have had a problem show up several times when including torsional design in my models. I will get a stress ration of say 1.19 for a certain member. I then increase the members size to lower the stress ratio to say .80 without clicking design again. Yet when I re-analyze the model the stress ratio jumps back up to around 1.19. This pattern continues to ridiculously large members, however, if I switch to a smaller member and re-analyze the stress ration drops again but never below 1.00.
It would be good to have an example and confirm your version.
It could simply be that having a stiffer member leads to the member attracting more torsion and hence a vicious cycle.