Dead Rabbit, it is normal for TWH's to have a footfall pattern so that their hind reaches out beyond their forefeet; however, they should swing out so that they don't hit them. This is not something that you train them to do; they just do it.
One of my arab mares used to click her hind into her fore constantly. She did it worse at the walk than at the trot. It annoyed me more than it did her. My farrier changed the angle of her back hooves. He shortened them up and made the angle a bit more steep. (When I bought her, she had a weird shoe job.) He also sets the back shoes so that she has about a millimeter of toe that goes beyond the front of the shoe so that if it does hit, it doesn't give me that annoying click.
I would talk to my farrier about it and if he is good, he should be able to help. It may take several shoeings.