I had been messing around with the new rabbits (which are very awesome by the way) and I decided to summon a Killer Rabbit with a command block. I used this code:

 /summon Rabbit ~ ~1 ~ {RabbitType:99,CustomName:"The Killer Rabbit of Caerbannog",CustomNameVisible:1,Attributes:[{Name:"generic.maxHealth",Base:1000},{Name:"generic.followRange",Base:500}]} 

As soon as The Killer Rabbit was summoned all mobs around me stopped moving. If I walked into them they would push me aside and if I destroyed the block below them they would float (I could still destroy blocks normally).

I started a new world and summoned a normal killer rabbit with a command block and without one and everything worked fine. As soon as I would try using the first code the same problem would occur again.

I also realized that the problem would only occur if I attacked the rabbit. As soon as I did all the mobs would freeze. I have attached 2 pictures of the floating killer rabbit.