If he was trained aversively for shutzhound, it may be that he has come to associate training sessions with punishment. I think the best thing you can do is stay the course. Pay attention to his body language and work at his pace, the PR training should really give him confidence in you and himself.
For the stand for show, are you molding him? You could also throw in some general counter conditioning to handling and your hands coming over his body just to help him relax.
Honestly though, I think time will sort this out