Players in spectator mode can have boats land on top of their heads, even though they shouldn't be able to interact with entities.

The way I showed this bug was by having a hole in the ground big enough for boats to fall into the void, and an always repeating command block in the center with the command /summon minecraft:boat ~ ~-1 ~

When I went underneath of the river of boats and they stopped. Going into third person showed that the boats were indeed landing on top of my head, even though I was in soectator mode.