The bug

When using a grindstone it always sets RepairCost:0 in the NBT of the item (except for books, see MC-148476), even though that is redundant because 0 is the default if no value is present.

Due to MC-129057, this prevents the recipe book from using such items (e.g. bow for dispenser recipe or fishing rod for carrot / fungus on a stick) because it does not ignore RepairCost:0 and therefore considers it custom NBT data, which should prevent using the item for recipes.

Reproduction steps

1. Put a bow in your mainhand and enchant it

   /enchant @s minecraft:unbreaking
   

2. Put the bow in a grindstone and remove its enchantments
3. Try using the bow as part of the dispenser recipe by clicking on it in the recipe book
   It refuses to use the bow
4. Inspect the NBT data of the bow by putting it in your mainhand and running

   /data get entity @s SelectedItem
   

   The NBT data of the bow contains RepairCost:0