I was messing around with the Test Tube and I placed lots of different elements into it. I was informed that I had managed to create Abbasidose, and was given XP accordingly. When I checked the Alchemistry Kit, I had Abbasidose in there, but also Diabolic Acid, which I had never created before. This didn't appear in the recipe book and I didn't receive any XP for it.
When I looked at the image, I decided to recreate the Diabolic Acid compound, and this time I received the XP for it, and it appeared in the recipe book. I now have two Diabolic Acid compounds in the Alchemistry Kit. The first unintentional, unrewarded compound, and the second intentional compound. The game has recognised them as the same and stacked them though.