Duplication Glitch?

Solution 1:

You do not have to do anything else to get the effect. You can see that it gives double results in crafting if you craft something. Instead of saying something like "You have crafted a knife", it will say something like "You have crafted a knife (x2)." You will also see that the number of the thing crafted will increase by two rather than one. Or in general by an even number that is double the normal results of the recipe.

It may be worth noting that the research upgrade that eliminates the use of materials when you craft is generally more useful. You can click the button as many times as you want then without losing anything.