OBX: A rental mystery

An entrepreneurial friend bought and fixed up a house on the Outer Banks, and this is the first summer he has rented it out. He and his family finally got to enjoy a week down there, and he was astonished to discover that one of the tenants had reversed several of the bedroom door locks. It was an easy fix, he said, but it creeped him out. And why wouldn't the tenants just put them back the way they were when their vacation week was over?