Entities bunched up together push other entities too much

Please describe the bug according to the guidelines and provide exact steps to reproduce.

I've just saw https://youtu.be/D_53rB_I3mo on youtube.

So basically:

1) Get a lot of entities in the same place and make sure they can't escape
2) Drop a player near it (make sure nothing blocks the movement of the player as well)
3) Get insta boost

These entities seem to push each other away while they can't (they are blocked in). If an other non-blocked entity gets near, it could get shot away a big distance at insane speeds.

Not confirmed this myself, but at least it should be easily duplicate-able.

can't reproduce in 15w44b unless I'm doing it wrong

Fixed in 15w45a.

Can still confirm in 15w45a:
http://gfycat.com/AjarFoolishAracari

Please reopen.

There's still strange behaviour connected with the NoAI-tag (in 15w50a):
https://youtu.be/YYX75Fppdz4

@unknown all current behaviour with the no ai tag is intended, also this is resolved as intended...