When standing on a boat if you jump multiple times every jump will build up fall damage and it seems to have to limit, jumping twice on top of a boat then onto a block causes half a heart damage from falling, ten times and you lose half you're health, i think when you jump on a boat you're momentum is kept even though you're standing but if you jump enough times you will actually take fall damage on the boat. i could not find any other reports about this bug.

Ok i just got in then out of a boat and suddenly this bug is not happening anymore
it is just happening randomly and might require multiple boats