To reproduce:

1. Give yourself all recipes (/recipe give @p *), place a furnace, and open the recipe book
2. Right click the iron ingot recipe and observe that the alternative input options are displayed as an overlay (because these are separate recipes)
3. Try to right click the iron nugget recipe and observe that nothing happens (because this is one recipe with multiple inputs specified)

This also happens when the multiple inputs are specified as an item tag instead of as specific items, like it is the case for the charcoal recipe.