The progress bar of furnace displays wrongly after reload the game

The progress bar of furnace displays wrongly after reload the game.

How to Reproduce:

At first, put some objects like Raw Irons in furnace and smelting it.

Then exit the game before the furnace is completed.

Reloading the game and open its GUI.

 

You can see that the progress bar displays wrongly, just like it can only smelt one thing. But actually it doesn't influence the number of objects.