The bug
Turtles go upwards when you feed them seagrass when they are in water. However, since 1.13-pre5, they fall down into the water upon almost being out of the water. Before 1.13-pre5, they did float in air while feeding them seagrass.
How to reproduce
Spawn a baby turtle near the surface of water
Feed the baby sea grass by holding down 'use' while aiming at the turtle
→ ❌ Keep aiming at the turtle, see how it goes upwards and falls down upon almost being out of the water
Attachments
Comments 5
They actually start to float out of the water and into the air if you hold down with the sea grass. so I think it's almost certainly unintended.
Was able to re-create this on Minecraft 18w07c.