Factorio Forums

Found through Randotorio.
viewtopic.php?p=486916#p486916

Different Smeltables with the same ingredients creates a conflict where one of the recipes can't be used because there is no way to select a furnaces recipe like you can an assembler.
E.g. if iron plates and copper plates both use the same ingredient, iron-ore each.
Mods can work around this, but it still seems like something that should throw an error?

Its not worth the hassle

Furnace recipes can have the same ingredients, but for many reasons, not be a problem,
For instance if they are with different recipe categories,
or If a mod script enables and disables them with precision.

Check with your own code, because this isn't really a problem for the base game