So I was messing around with boats when I found a bug. If you place a boat on the highest pixel on the top pixel on the side of a block it will place the boat as if it is on top of the block, but the boat says it's on the side of the block so it falls through.

How to recreate: Make a 3-tall pillar and break the first two blocks. Then place the boat on the highest part of the highest pixel on the side of the block.