When a golden hopper inserts fuel items into the side (or front or back) of a furnace, the item disappears from the hopper's inventory but is not added to the furnace's fuel slot. The item is (apparently?) permanently lost.

Other observations:

• The problem (attempting to insert fuel item and losing it) occurs even if the fuel slot of the furnace is full or contains a different item.
• Normal iron hoppers behave as expected (fuel items inserted into the side of a furnace appear in its fuel slot)
• Non-fuel items behave as expected (neither golden hoppers nor iron hoppers attempt to insert non-fuel items into the side of a furnace)

Environment:

• Java 17.0.1
• MC 1.18.1
• Forge 39.0.44
• GoldenHopper 1.2.5-1.18.1
• No other mods are installed