Teleport with RetainPassengers flag doesn't appear to retain passengers.

[ShaneBeee]

Expected behavior

I would expect the passengers of an entity to be able to teleport

Observed/Actual behavior

I noticed when a player is riding an entity, if you teleport it (with flags) the player doesn't get teleported.
The player also gets stuck in some weird limbo.
For example if you move a few chunks, the chunks no longer load, and if you attempt to break a block, nothing.
If I relog, the player is then matched up with their vehicle.

Steps/models to reproduce

Test code to reproduce:

Random random = new Random();
Entity vehicle = player.getVehicle();
World world = vehicle.getWorld();

int x = random.nextInt(10000);
int z = random.nextInt(10000);
Location highest = world.getHighestBlockAt(x, z).getLocation().add(0, 1, 0);

vehicle.teleport(highest, TeleportFlag.EntityState.RETAIN_PASSENGERS);

I simply make myself ride a sheep, and ran a command with that code.

Plugin and Datapack List

[18:17:09 INFO]: Server Plugins (1):
[18:17:09 INFO]: Bukkit Plugins:
[18:17:09 INFO]:  - TestPlugin

Paper version

Paper version 1.21-39-master@aa8d38d

Other

When looking at vanilla NMS Entity#teleportTo, I see they do the following:
(not sure if I can show Mojang code here, so ill just write short form)

this.moveTo(...
this.teleportPassengers();
this.setYHeatRot(...

For testing sakes, I decided to incorporate this into CraftEntity's teleport method:

Did a quick build, and did a few simple test runs, the code I provided above now seems to work flawlessly.

[stitchinger]

Yep, this is still happening.
Teleporting a player is not happening with passenger and RETAIN_PASSENGERS flag