I had like 500 cobble smelting in every furnace when the blacksmiths ate a little, at which point they abandoned their furnaces. All the cobble disappeared from the furnaces. The already smelted stone and coal was still there.
#Blacksmiths removing everything in furnace when they eat.
sleek crest
west crescent
The furnaces usually don't work too well with more than 64 resources at a time. You are using yesterday's release, right?