When going slightly below a boat, you can notice that the boat floods as shown in the video attached.

How to reproduce

Start off by crafting a boat, then place the boat on water, go slightly under the boat, not completely under the boat just slightly. The boat will become flooded for some reason.

Observations: Boat floods for no reason when slightly below it.
Expectations: Nothing should happen, you're going below the boat, nothing should happen.