The same happens when you place it on top of a hopper
It also happends in 14w05a, when you enter spectator mode, you exit "inside" an entity (watching its POV) and you hit the entity outside of spectator mode, it outputs "Attempting to atack an invalid entity" (As in MC-46411 )
Worked for me. But I think this is a feature because it also happens in horses and minecarts. You dont consume hunger and you don't need to see it when you are ridin a vehicle.
Worked for me
I search it but it doesn't appear, sometimes it works a bit strange.
Also happens in survival, less common and a shorter delay