I've also seen Bela moving towards the path down the mountain a bit, but not very far. I also have the suspicion that Bela (and probably other vendors as well) gets alarmed when I fight a battle half across the wilderness, all of the monsters and npcs seem to have a fully functional radar sense.The T'Rang dealer down Marten's Bluff is the most notorious wanderer in my experience, he frequently moves all the way out of his room, following the slime trail. Sometimes a glitch occurs when he's about to pass the door, he will get stuck in front of the door, floating 2 meters above the floor and rapidly blinking in and out.