I believe the changing of hitboxes has caused some unforseen issues with the movement, and behavior of mobs. You used to be able to get cows to follow you through water, and onto land with no problems. Now this seems like an impossible task! I haven't tried any other animals, but I hope this gets changed as soon as possible because I would really hate for this to be apart of the game. 
Sincerly,
Candlestickking