A bug that freezes all the game and crashes it

Put the summary of the bug you're having here

What I expected to happen was...:
That if I summon a cow riding a boat with the /summon command, it will appear a boat above a cow.

What actually happened was...:
All the game freezes, but you can continue walking and building.Then I tried to exit to the menu and the game crashes.

Steps to Reproduce:
1. Put in a command block: /summon Cow ~ ~1 ~ {Passengers:[

{id:"Boat"}

]