[MC-96881] Player-ridden entities disappear on relog

Player ridden entities disappear upon relog, but only when the world is open to LAN upon getting on the entity and logging out.

1. Create a new singleplayer creative world
2. Open world to LAN
3. summon a minecart
4. get in the minecart
5. log out
6. log back into the world

the minecart will have completely disappeared.

Linked issues

Can't confirm for 16w06a

Only in the latest snapshot

I figured out what the bug is. It only happens if the singleplayer world is open to LAN upon getting into the minecart and logging out.

Confirmed!

Also happens with boats. Any entity the player is riding, really.

Confirmed for 1.8.9 as well. Also works on boats, pigs, and horses. I discovered the latter the hard way, lost my favorite horse!

What's with the environment change? Does this happen in multiplayer also?

@unknown it's littirally mentioned in the description

seems to be fixed in 16w43a. However, it also seems to be a duplicate of MC-47508