The bug
If a player is sitting in a boat and the boat is above an upwards bubble column, the boat will appear teleport two blocks upwards to the player in front of the boat.
To reproduce
Enter a boat
Enable F5 modeThis is not needed as shown by the video, can occur in first person as well.Row the boat on top of a soul sand bubble column
→ ❌ The boat will appear to teleport upwards
Video
Youtube video showing this bug: https://youtu.be/KuZAsq5W0zA
Can confirm this is an issue in 19w39a.