The bug
If you combine two armor pieces, and the second one is cursed, the resulting item will not be cursed (and you get no xp). It is specifically stated in the changelog that curses cannot be removed via grindstone.
Also, if the two items have different curses, only the first curse will be kept.
Linked issues
is duplicated by 1
Attachments
Comments 20
10 more comments
The mechanic works similar to the anvil, with a "main" input slot and a "sacrifice" one. Any enchantments or curses on the sacrifice will be lost regardless of the main item, as enchantments are not passed on through the grindstone. So if the sacrifice has a curse and the main item does not, the output will not be cursed. But if the main item has a curse, the output will have as well.
Initially I didn't think this was a bug, but maybe it is unintended result behaviour.