Possible to put stacked sword in the anvil

The bug

You can put stacked items that normally aren't stackable into the anvil, expected it to just put one item into the anvil. (Video by Capitão Black Shot)

How to reproduce

1. Give yourself 64 swords, and one enchanted sword.

   /summon minecraft:item ~ ~ ~ {Item:{id:"diamond_sword",Count:64b}}
   /give @p diamond_sword{Enchantments:[{id:sharpness,lvl:3},{id:fire_aspect,lvl:1},{id:looting,lvl:3},{id:sweeping,lvl:3},{id:unbreaking,lvl:1}]}
   

2. Put the illegal stacked item in the anvil.
   → Puts the 64 swords in the anvil, should put only one as its not stackable
3. Put the enchanted sword in the second anvil slot.
   → It valids the process; you can apply the enchantments to the 64 swords.