The bug
Steerable ridden entities like boats, pigs or horses teleport client-side to the position where you first started steering them for a short moment when you stop steering them. You can stop steering such an entity by either dismounting it or for example for pigs stop holding a carrot on a stick or for horses remove the saddle from the horse.
Video example: https://www.youtube.com/watch?v=ATXLXGaq-q8
How to reproduce
Start riding a steerable entity like for example a boat
Switch to third person view (
F5
) (back view) to be able to see the complete boatMove a while in it
Dismount it
→ You will see that the boat is teleported for a short moment to the position where you first started riding it
Code analysis
Based on 1.11.2 decompiled using MCP 9.35 rc1
The method net.minecraft.entity.EntityLivingBase.onLivingUpdate()
ignores all position and movement changes caused by the method net.minecraft.entity.EntityLivingBase.setPositionAndRotationDirect(double, double, double, float, float, int, boolean)
, which then, once the riding player is not steering it anymore, take effect. It might be good if the server would not send the packets calling this method if the entity is being steered or if this method would only set the field values if if the entity is not being steered.
Related issues
is duplicated by
Attachments
Comments

Can confirm.

Please see if 16w32a fixed this issue.
Still in the 16w32a.

confirmed in 18w07c.

Affects 18w22c

Just tested this on 19w38b singleplayer and it appears to still occur with boats. The boat even teleported back to the position it used to be in and stayed there without letting me get in. I was forced to save and quit and start up my world again

Here is a attached gif of the bug happening in 19w38b.
[media]This does indeed still happen in 19w38b. However, this ticket only describes the case in which the boat returns a short time after exiting. There's another issue with the boat never returning, which is MC-161313. That is the issue that @unknown is experiencing.