Coal gets consummed in furnaces when there is no need to

Put the summary of the bug you're having here

What I expected to happen was...:
I expected a normal consumation.

What actually happened was...:
Furnaces stop burning coal but, he still reduce. so i lost a certain ammount of coal.

Steps to Reproduce:
1. Place Coal and ore in furnaces
2. The furnaces start makes some materials like iron lingots...
3. Then sometimes, the furnace stop makes these materials, but we could see that the coal still be consumed.

I hope that i haver correctly described this bug, and i hope that you will understand my report, i appologise if i made some mistakes, i'm french

Thanks.
Regards, Thomas