Kevin Ghere

14w08a Has the original issue described, but the effect is different than the current issue. I believe the original bug was fixed before 1.8, but this new bug was introduced in the 1.9 snapshots, and people jumped on this thread. MC-97513 more accurately describes the current state of this issue.

I tested it, and the problem appears on 1.9. 1.8.9 seems to work correctly. I'm not sure what caused me to say this was a boat specific issue up above, since the problem in 1.9 seems to affect boats, pigs, and horses. It is still true though that it does not affect minecarts. Not sure why it was marked for 1.8.

Here's some other things I've noticed with this issue.

Teleporting boats more than 10 blocks away seems to work, but less will not move you or the boat.
Applying a velocity to a boat also does not work, and the boat will not move while a player is in it.
Teleportation DOES work on a boat if it is empty, or if it has a different entity in it, but not a player.
Teleporting minecarts / other rideable entities while riding them works completely fine. It seems this is a boat specific issue, possibly caused by the new boat mechanics / latency code.

Also, if you summon a boat riding a boat, teleporting the boats when the player is in top(controllable) boat will do nothing, but sitting in the bottom(uncontrollable) boat results in both boats + the player being teleported correctly.

I've been messing with this for a bit, and the bug still exists.

Teleporting a minecart with a player in it works fine.
Teleporting a boat with a player in it doesn't work.
Teleporting an empty boat or a boat with a mob (I tested with a pig) in it DOES work.
Teleporting a boat with a player in it DOES work IF the boat is teleported more than 10 blocks away.

This is obvious strange behavior, since teleporting minecarts is fine. I believe this might be caused by the boat desync optimization done a while ago. This would really help a project I'm working on if fixed.

Tested in 1.9 pre2.