Bizzare Endermen behaviour / no-aggro

This has been an issue in the last few snapshots, but due the rare appearance of the E-men, I wasn't sure. I am unable to aggro the E-men. I look at them, they display the anim, emit the sound, then teleport away. Today I chased one all over the desert, it refused to come to melee. Then, another tp'd onto the bent trunk of an acacia, fell off (showing damage), then walked into a wall and stayed stuck there until I hit it. This time, no aggro was displayed until hit, and there was no scream.