Until 15w36a, the Shulker collision was fine. In 15w36a, collision being added to many entities, the Shulker gained the ability to push mobs away from it. Now, even though the Shulker was supposed to have collision much like a block, it now pushes other mobs away from it, making it to look strange as a block-type mob. I'm not sure if you could consider this a bug, but I think it should be taken as one.

What I expected to happen was...:
The Shulker to have a collision like a block.

What actually happened was...:
The Shulker pushed other mobs away from it, even if they didn't touch the Shulker itself.

Steps to Reproduce:
1. Spawn a Shulker.
2. Try to come near it or jump on it.

Video: https://www.youtube.com/watch?v=VTv_d4jc1rI&feature=youtu.be