Furnace bug

Put the summary of the bug you're having here

What I expected to happen was...:
You can switch the slots in the furnace for what you you want to smelt and fuel

What actually happened was...:
It wouldn't let me switch the slots, or take anything out.

Steps to Reproduce:
1. Pressed on the furnace
2. Press on fuel slot
3. The selected slot didn't change, I could only put in something to smelt.

P.S. Sorry if it's confusing, it's hard for me to explain.