During a fresh normal survival world, an Enderman entered my docked boat at the shore near my home. This by itself is not strange, but when it Is stared at (and hit) it could teleport outside the boat and somehow kill me at a distance even though the Enderman is still inside the boat, visually. So basically the teleported Enderman is invisible.

This also allows other mobs to enter the boat even though there is already an Enderman there. like a creeper or even the player.