Ever since the AI changes in the early 1.8 snapshots, Endermen AI has been buggy in multiple ways.

1. When an Enderman teleports, their pathfinding does not account for it. As a result they will often pathfind to the spot they stood before teleporting. This can turn into an endless loop.

2. After taking player damage, Endermen lose the ability to teleport in order to dodge melee and environmental damage such as water. They will not dodge sword hits or teleport out of water/lava. They seem to still dodge arrows however.

3. Endermen deaggro after losing line of sight

4. (May be related to a separate, general bug) Walk at a glitchy fast speed