Water Breathing from a turtle shell depletes even while riding a nautilus

When a player is riding a Nautilus, water breathing provided by wearing a turtle shell helmet depletes.

Put on a turtle shell in survival mode and go underwater on a Nautilus. As soon as you are submerged, the water breathing starts to deplete.

Turtle shell water breathing should either be paused while riding a Nautilus, or reset when the player dismounts it.

Instead, when you dismount the Nautilus, you have no water breathing buffer left.