When the player boards a boat, leaves the boat (any distance) and reopens the world. The player is then teleported into the boat they just left.
Steps to duplicate (it's good to start fresh when testing.)
-Start a creative world.
-Get into a boat.
-Use the boat a little.
-Leave the boat.
Reopen your game. You will then be teleported into the boat you just left.
also happens to me in survival mode