When endermen fall a long way through a 1 block wide drop shaft, at the bottom they will often glitch into adjacent blocks. Doesn't matter if the drop shaft goes all the way down or stops at their head height. If the blocks at their head height are solid they will also glitch into them, but die.

This has been a problem at least since 1.8, but for some reason the version selector won't give me anything below 1.9.4.