A script error appeared during a crafting session. Details should be readily apparent in the screenshot below. Please let me know if you need further information.
(https://i.imgur.com/RVyJmQc.jpg)
I had this bug happen to me too, and noticed that when it happened the recipe didn't "end". If I kept using the table the previous added items would still be there and additional items would continue the existing recipe, causing me to add too many items.
This is a very unfortunate bug that has existed since the start of COR, it seems pretty much isolated to the Oil Flasks.