I had items smelting in a furnace the last time I signed off (Single player running the previous snapshot) and the next time I logged in was after I upgraded to 14w04a. The furnace continued smelting and consuming coal but the iron that I was smelting remained in the first slot and stayed as an ore, never turning into ingots. Even after taking items out of the furnace and putting them back in, the same thing happened. It did not fix itself until I broke the furnaces and re-placed them.