I created an enchantment which is listed as a curse, but is incompatible with Curse of Vanishing. This works properly in the anvil.

However, when combining two items, one with my curse and one with Curse of Vanishing in the crafting table/survival crafting grid or a grindstone, both enchantments are placed on the same item, without regards to their incompatibility.

I believe that, as these two curses are incompatible and that incompatibility works properly in an anvil, it should also function when repairing items via crafting or in a grindstone.

How to reproduce:

1. Create a world with the attached data pack (MC-274663.zip).
2. Give yourself two enchantable items of the same type.
3. Enchant one of them with Curse of Vanishing and the other with the data pack's Example Curse enchantment (example_curse_incompatibility:example_curse).
4. Try to combine the two items in an anvil.
   → The anvil doesn't let you combine the items as the enchantments are incompatible.
5. Try to combine the two items in a crafting grid or a grindstone.
   → The items can be combined, resulting in an item with incompatible enchantments on it.

Expected result:

Two incompatible curse enchantments would not be able to be combined by repairing two items in a crafting grid or a grindstone.

Observed result:

Two incompatible curse enchantments can be combined by repairing two items in a crafting grid or a grindstone.