Converting a single copper block to any variant in the stonecutter causes 4x of variant output. Doesn't matter if it's Cut, Chiseled, Grate, Stair, or even slabs. 4x the result (slabs will show 8). Check out the clip I've attached. I have even displayed F3 to show this is vanilla directly.

Reproduce:

1. Make copper block
2. Place block in stonecutter
3. Observe output is 4x no matter the variant.

EDIT: Provided screenshots of crafting the Cut Copper from the Crafting Table compared to the Stonecutter.