I summoned two animals with minecarts on top of them.
I made one animal move towards the other with the /tp command.
Once it bumped into the other animal, the game bugged out.
Steps to reproduce:
1. Create a superflat world.
4. Put this in a command block(Repeat/Unconditional/Always Active) :
5. When the animals collide, the game becomes buggy (can't run commands, can't exit world, etc.)