Not really duplicating, but it just crafts Smooth Sandstone a ton of times.

I was playing around trying to make the creeper faced sandstone, and I didn't expect anything to happen.

It just created 4 smooth sandstone, out of 4 smooth sandstone

Steps to Reproduce:
1. In a 2x2 crafting grid, put 4 smooth sandstone in all of the grid.
2. Recieve 4 smooth sandstone