I thought I hadn't found Mabon yet and got in a loop of trying to invent it when I already had - it told me the combination didn't work.
Later on, when I'd picked up some more ores and crushed them, it was there. But it would be helpful if the test tube could let you know that you tried to invent something you already know.
Rueful: It looks like you've worked out the problem, but it's helpful in the future if you list the specific elements you're trying to combine so it's easier to figure out if it's a bug or if you're doing it incorrectly.
shhexycorin: I'll see if there's a better way we can handle it, like asking if you're trying to make something you've already made.
I think to maintain the spirit of experimentation we're going to leave it as it is, however in the future if you're trying to learn something and you've learned all possible combinations with a given set of elements, we'll inform you more clearly that there's nothing left to learn. This is a slightly more specific response than saying the combination didn't work, and it should prompt people to check and make sure they didn't already learn it.