Summary
If a single unenchanted tool is placed into the input slot of a grindstone, the tool appears in the output slot and can be selected, even though the tool did not have any enchantments or need any repairs.
Steps to Reproduce:
Place down a grindstone.
Open the grindstone GUI.
Place a single unenchanted tool in the input slot.
Observed Results:
The tool appears in the output slot and can be selected despite it being unenchanted and fully repaired.
Expected Results:
The tool doesn't appear in the output slot and an "X" is placed over the arrow.
I believe this is just an Overlooked feature that fixes some problems during development