Anything you put in a furnace cannot be taken out.
What I expected to happen was...:
Normally, anything you put in can be taken out.
What actually happened
I went to burn wood, changed my mind, and could not take it out. So I burned it, and could take nothing out.
Steps to Reproduce:
1. Place wood or iron in the top square of a furnace.
2. Try to take it out.
3. Add coal to the bottom and try to take it out.