Minecraft 18w15a, Minecraft 18w16a, Minecraft 18w19a
- Spawn a dolphin
- Give yourself some armor
- Throw them at the dolphin
→ See the dolphin pick up the armor, but not drop it again like any other item.
This applies to other armor too.
The bug is also shown in the nbt of the dolphin in ArmorItems, when you run the command /data get entity @eArmor[limit=1,type=dolphin] ArmorItems