I was playing today on Steam and while in a shop I was trapped when I moved to the far side of the room, putting Brax in the fog of war. He "teleported" while out of line of sight to stand in front of the exit. No potions or skills to teleport so I guess I'm stuck.
You probably picked up an item and haven't payed for it-- sometimes even if you put it back, Brax won't move. Then you have to pick up another item and put it back on the pedestal to get Brax to move out of the way.
No, no items were purchased/picked up. I did drop and retrieve some items in the room, but not on to or off of pedestals.
I have accidently dropped a trap (from my inventory) and had brax block my exit when I picked it back up. It was quite a headache to get out. On a slightly related note, there is a youtube video showing how you can move stuff around to take stuff in and out of the shop (haven't done it myself since it is definitely a bug and not a feature):
