I made a short, 2-block wide, 1-block deep, path of water going east-west. I got in a dark oak boat at the west end, rode it to the east end, and got out. After I got out, the boat rendered back at the beginning of the path and then quickly moved towards where it should be. I tried this several times on the same path and it did the same thing. The boat rendered as normal when I rode on that path east to west. I am attaching a video file showing exactly what happened.