Can't put coal or anything in bottem bit of fernace

Put the summary of the bug you're having here

What I expected to happen was...:
You could click on the bottem box in fernace and put coal in it

What actually happened was...:
The box thing doesn't react to clicking it and can't not cook anything

Steps to Reproduce:
1. Make a fernace
2. Put something that's cooks in the top bit
3. And put coal or something in but it won't let you