Put the summary of the bug you're having here
*What I expected to happen was: smelt birch wood into charcoal
*What actually happened was: crash. The game closed with no loss of world data.
Steps to Reproduce:
1. Put charcoal in the bottom (fuel) slot of a furnace
2. Put birch wood in the top (input) slot of the furnace
3. Wait for wood to smelt
Note that this does not happen with normal oak wood. I have not tried it with any other fuel or with pine wood.