The bug

I was playing around with a baby turtle with a high level of thorns on it and it seems to one-shot every mob except the ocelot and cat. They don't seem to take damage from the thorns enchantment.

To replicate this, summon a baby turtle wearing a thorns enchantment and spawn a cat or ocelot near it to attack it. You would expect the cat or ocelot to take damage from the thorns but it doesn't seem to work like that. This is goes against other mobs that attack the baby turtle that do take the thorns damage.

To reproduce

1. Place a command block.
2. Enter the following command:

   /summon turtle ~ ~1 ~ {Age:-25000,HandItems:[{Count:1,id:diamond_sword},{}],ArmorItems:[{Count:1,id:diamond_boots,tag:{Enchantments:[{id:thorns,lvl:3}]}},{Count:1,id:diamond_leggings,tag:{Enchantments:[{id:thorns,lvl:3}]}},{Count:1,id:diamond_chestplate,tag:{Enchantments:[{id:thorns,lvl:3}]}},{Count:1,id:diamond_helmet,tag:{Enchantments:[{id:thorns,lvl:3}]}}]}
   

3. Summon a zombie.
4. Notice how the zombie takes Thorns damage upon hitting the baby turtle.
5. Kill the zombie and summon a cat.

Observed result

The cat doesn't take Thorns damage.

Expected result

The cat would take Thorns damage.