Furnace stops smelting

Hi,

In this latest snapsot for JE, three times my furnace halted smelting process. For the first and second time, I inserted 24pcs of cobblestone and 16 wood planks.  For the third time, inserted 3 stones and 2 wood planks. Result: In the first two cases, only 22 stones were created. In the third case, only one smooth stone created. Need to fix quickly, smelting is an essential part of many block production.