Endermen aren't careful enough around water (or lava) and sometimes run straight into it. I believe this is new behavior.
It might also just be because of it's speed, and any other mob would fall into lava if they were as fast, but it's still probably not intentional as they are supposed to avoid water and lava.
How to reproduce:
Aggro an Enderman and go in a pool of water, where the edges are like in the attached examples. The Enderman needs to run off a higher block to drop into the water.
Punch the Enderman to make it teleport, and move around, to get it run into the water.
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I've managed to reproduce the bug, and here's what I can tell:
This bug is related to how endermen react to falling down a block. If the shore is level next to the water, the enderman will not fall in. This only seems to affect endermen moving diagonally, and not in the cardinal directions.
To reproduce effectively, you can use the following setup (Gold blocks are where the player stands, diamond is where the enderman should spawn).
Relates to MC-198674
Can't replicate. Enderman won't come into the water, even after punching.
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