Grindstone could increase repair cost of items with curse enchantments

If you use grindstone to disenchant an item with curse enchantments, the repair cost could be increased.

Step to reproduce:

1. take an enchantment book with binding curse from creative inventory, and another with vanishing curse.

2. combine 2 books using anvil.

3. middle click the combined enchantment book to copy it, and put the copy into grindstone.

4. using /data command to check their repair cost: the repair cost of book with 2 curse enchantments is 1, but it becomes 3 after processed by grindstone.