By using Command Block or just using commands in chat, i can make a minecart / boat to ride a mob. For example using this command:
/summon Minecart ~ ~ ~ {Riding:{id:EnderDragon}}
By doing that, I can ride the minecart, so it appears that i am actually riding the mob under the minecart.
So i will just ride the minecart to make me looks like riding the mob.
And here is the bug:
While riding the minecart on top of the mob and if I quit Minecraft
After that i played on that map again, suddenly the mob i am riding is gone. What is left is me, riding on a minecart. The mob under minecart is gone.
Here is how to replicate the bug
1. Summon a minecart / boat that is riding a mob, using a command block or command chat.
2. Ride the minecart / boat
3. Return to the main menu or quit Minecraft.
4. Play on that saved game again.
5. Mobs that was ridden by minecart is gone.
Related issues
Comments

Duplicates MC-10343