Put the summary of the bug you're having here Put any items into furnace slot (fuel slot and smelt slot) with a comparator facing it , it exits gui and when you re-open the furnace items gone.

What I expected to happen was...:For it to give out a signal from the comparator
Describe what you thought should happen here

What actually happened was...:It Exits you from the gui and when you re-open the furnace the items are gone.
Describe what happened here

Steps to Reproduce:
1.Put a furnace on ground
2.place a comparator next to the furnace.
3.Put any items in the smelting slot and fuel slot and in a second it exits the furnace gui
4.Re-enter furnace and items are gone!