Can't use a furnace.

Put the summary of the bug you're having here
The furnace won't let me change slots or take stuff out.
*What I expected to happen was...:*nothing
Describe what you thought should happen here
It should have let me swap slots and take stuff out.
What actually happened was...:
Describe what happened here

Steps to Reproduce:
1. Open Furnace
2. Tap Slots
3. ...