If you drive a boat on land and then get out later, the boat is randomly teleported somewhere else or to the mounting position. I could not say exactly yet.
In addition, you can not move anymore. I'm stuck.
Boats sometimes teleport when exiting
Donkey floats in air when dismounting/dismounted by water
Horses are quite messed up
свиньи имеют летать - pig can fly
Boat Glitch (In more detail)
The boat or the horse disappears when getting off
Horses, donkeys, mules, and boats sometimes disappear after dismounting
Steerable ridden entities (boats / pigs / horses) teleport back to their previous position for a short moment on dismount