So I was playing shortly after the 0.7.0 update and decided to make some glass. I opened the furnace and was able to place sand into the ingredient section. Unfortunately, I could not select the fuel section to take coal out, I could not click the final product (in this situation, glass), nor could I remove sand from the ingredient.
To reproduce: open a furnace with fuel in it, then place sand or any substance in the ingredient. Then try to remove it. Try to remove the fuel. Try to remove the final ingredient. None of this is possible.