Similar to MC-271252, bucket entities lose all equipped items (held items and armor items) when picked up and replaced with a bucket.

How to reproduce

1. /summon tadpole ~ ~ ~ {ArmorItems:[{},{},{},{id:"minecraft:iron_helmet",count:1,components:{"minecraft:enchantments":{levels:{"minecraft:thorns":255}}}}]}

2. In survival mode, attack the tadpole to confirm it has a helmet enchanted with Thorns
3. Pick up the tadpole with a water bucket
4. Place the tadpole back down
5. Attack the tadpole again in survival mode

Expected result

The tadpole would continue wearing the helmet with the Thorns enchantment.

Observed result

The tadpole no longer wears the helmet enchanted with Thorns, so you won't take damage when attacking it.