Source block contents changed when dropping loot from loot table with "set_attributes" function

The bug

When using a loot table with the entry type dynamic and the entry name contents combined with the set_attributes function on a shulker box with the /loot command, the function also changes the items inside the shulker box.

How to reproduce

1. Put the attached loot table into a loaded datapack at <datapack>\data\minecraft\loot_tables\blocks
2. Place a blue shulker box and fill it with a diamond helmet
3. Step on top of the shulker box and type the command /loot give @s mine ~ ~-1 ~ in chat

This should leave the former item unchanged and create a new one with modified attributes.

Instead, it will cause the diamond helmet inside the shulker box to also only have +2 Armour unlike the former diamond helmet which had +3 Armour and +2 Armour Toughness.