Summary

Using the /tp command on some ridden entity types will teleport the entity and the riding player up as expected, but on other entity type the tp command will simply do nothing despite saying it has teleported the entity in chat.

Details

When testing the /tp command with boats, boats will fail to teleport if player is within the boat, and nothing will happen; however, the command output in chat will still state the entity has teleported to the given position. This behavior also extends to horses, regardless of if the horse has a saddle or not.

However, this behavior does not affect entities like minecarts and pigs; running the /tp command when the player is riding either of these entities will still successfully teleport the entity.

This is also partially a parity issue as this issue is not present within Bedrock Edition, however at its core it is still an inconsistency in behavior and a bug as there is no error message given from the /tp command when this is done, despite the teleport failing.

Replicating the Error

To do this, simply summon a boat (or horse), ride it, and run a /tp command targetting only the summoned entity, e.g.

/execute @e[type=boat] at @s run tp @s ~ ~5 ~