my 4th run with one of the bottom furnaces having deleted its inventory
can confirm for 13w05b. I am running win8. I used a 4x4 wall of furnaces feed from behind using hoppers at the very top I used doubechests to keep the hopper topped of. My fuel was sticks.
1st run smelting 64 in each furnace one stack was deleted.
2nd run 2 stacks where deleted
3rd run nothing was deleted
4th run 1 stack was deleted
each time it deleted the fuel, smelted and unsmelted items in the furnace (attached a image with my setup this was the 4th attempt right after one of the furnaces deleted their inventory
Same thing happens with nether portal blocks