The bug

Killing a horse wearing armor with a looting 3 enchanted sword has a very small chance of dropping more than 1 armor.

How to reproduce

1. Get an item with looting on it

   /give @p minecraft:stick{Enchantments:[{id:"minecraft:looting",lvl:100},{id:"minecraft:sharpness",lvl:100}]} 1
   

2. Summon a horse with armor

   /summon minecraft:horse ~ ~ ~ {ArmorItem:{id:"minecraft:diamond_horse_armor", Count: 1b}}
   

3. Kill the horse with the item that has looting
   → The horse dropped two horse armor