Items in the armor.body and saddle slots are not kept when dying while the game rule keepInventory is set to true

Steps to reproduce:

1. Equip an item into armor.body slot:
   /item replace entity @s armor.body with minecraft:diamond_horse_armor

2. Equip an item into saddle slot:
   /item replace entity @s saddle with minecraft:saddle

1. Check if item is in the armor.body and/or saddle slot:
   /data get entity @s equipment.body
/data get entity @s equipment.saddle

2. Changing the gamerule keepInventory to True:
   /gamerule keepInventory true

3. Kill the player:
   /kill @s

Expected Result:
/data get entity @s equipment.body returning item stack, meaning the slot still has the item.
/data get entity @s equipment.saddle returning item stack, meaning the slot still has the item.

Actual Result:
/data get entity @s equipment.body returning fail with the description of: Found no elements matching equipment
The item is also not dropped on death, so it completely vanishes.

/data get entity @s equipment.saddle returning fail with the description of: Found no elements matching equipment
The item is also not dropped on death, so it completely vanishes.