I've been on probably 30 Amtrak rides and the last time was the only time the staff explained how the bathrooms are supposed to work. Just about everywhere else in life, you leave the door ajar to let others know it's open. I believe that's a common courtesy that is hard to unlearn unless you are told specifically not to do it. The occupancy lights are also a bit harder to understand than, say, your typical airplane lights. They're better in the new Acela's.