Dropped a mine, then picked it back up. It apparently makes him think you just stole something. Blocks door. I was seperating some mines to sell them singly, as I noticed doing so gets more money. Now I'm stuck with a character I don't want to lose in a shop I can't leave unless I actually attack brax.... or find a way to trick him into moving away.
Ok, I solved the problem myself, but it's still a bug to be reported. I ended up picking up a steel ratchet crossbow, put something in its place, then did some fiddling around to place the crossbow outside his shop, which I believe is another bug that's fishy. SO. Guess learning about this bug paid off!