The furnace is not working

Put the summary of the bug you're having here
Furnace won't work
*What I expected to happen was...:*to add coal to the furnace to

*What actually happened was...:*the second slot for fuel,would not allow me to add the fuel.
Describe what happened here nothing happened as it would not work

Steps to Reproduce:
1. Added iron block to furnace
2. ...tried to add fuel..coal
3. ...would not accept coal as fuel and the iron block got stuck could not remove.
4 tried to retrieve the block but had to destroy furnace to get it back. Tried several times to make iron in furnace but won't work.