Furnace Fuel Square Bug {IMPORTANT}

As I was playing my survival world, I created a furnace and needed to smelt some cobble. I am able to put wood in the top square (to test it), but unable to access the bottom square.

What I expected to happen was...:
I expected to access the bottom square (in the furnace) to put some wood to smelt cobble.

What actually happened was...:
I click it, and it doesn't select the square and doesn't give me the option to access it in any way.

Steps to Reproduce:
1. Make a furnace.
2. Add >insert smeltable material of your choice< in the top square.
3. Try to put some fuel. (It won't let you access the fuel square)