Vendor Recipe - Gemcutters Prism Inconsistency

Just tried to vendor ten gems with each 12% quality which results in 120% quality, that diverted by 40% (as needed for a GCP as return) would be three GCP. But for some odd reason it results in two GCP and two scroll fragments.

First I checked that all gems I was about to vendor have the 12%. All do. Thus no error here.
After that I tried different gem setups (removed two Vaal gems and added two normal ones instead). Same result, two GCP and two scroll fragments. Next I made sure that there are no duplicate gems in the setup, but that did not change the result.

Also if I add another two 12% gem to the setup (twelve 12% gems for a value of 144%) the result changes to the previously expected three GCP.
I know for certain that with up to 80% it works without discrepancy but somewhere above that the algorithm seems to produce wrong numbers.

Update: Gave it a thought. As I see it the quality value of each gem is being added until it reaches the threshold of 40% or more and resets the total value to 0. That way the calculation would fit for the result.

0 + 12 + 12 + 12 + 12 = 48 -> 1 GCP -> 8 + 12 + 12 + 12 + 12 = 48 -> 1 GCP -> 0 + 12 + 12 = 24 -> 2 Scroll Fragments (one for each of the remaining gems)

Guess it is like this. But on the other hand in my opinion this way to calculate it is wrong if one GCP/AS/BW is to be granted for each 40% of quality provided.

That's because the recipe is 40% for 1 gcp, not 80% for 2 or 120% for 3 or any other multiples of 40 for any number of gcps. One item cannot be used in two recipes at once so you can't take part of one gem for one recipe and the other part of the gem for another recipe. Not a bug.

"

That's because the recipe is 40% for 1 gcp, not 80% for 2 or 120% for 3 or any other multiples of 40 for any number of gcps. One item cannot be used in two recipes at once so you can't take part of one gem for one recipe and the other part of the gem for another recipe. Not a bug.

Thanks for the clarification.
No Bug: Matter is resolved.