Item duplicates in furnace

I put some items in a group of furnaces underground and unloaded them at a later time. After travelling far away and coming back with more items to put in the furnaces I found that the items that I had previously taken out had been duplicated. This is what I have done and observed:
The items duplicated were iron, stone, and glass
I had gone back to the main menu multiple times in a short period but never closed the game.
I was able to replicate the bug only twice by going to the main menu right after withdrawing the iron from the furnace.
I hope this helps.