on galaxy s6 - my furnaces stop smelting items when I leave to explore other places in my world. If I leave walk far enough away so that the furnace is in an unloaded chunk, the furnace stops processing. In mpce 14.3 and before when I would go several biomes away the furnace would have processed everything, but now when I come back it only has a few items. Seems to be that the furnace stops processing when the chunk it is in is unloaded. It smelts at regular speed when it is in an active chunk.
This works as intended and has not changed for a long time. The behavior you are describing from 0.14.3 seems incorrect. In 0.14.3 and earlier, all activity stops in unloaded chunks.