They fixed this with the FF update

Please fix this

It is hard to tell which part of the deck check is actually broken.
As mentioned in OP, inside the deckbuilder it works fine (no "craft all" button).
Immediately after crafting, there was a warning when saving the deck ("deck contains cards missing in your collection"). After a while and testing with decks for different formats (tested Brawl and Timeless), this warning disappeared everywhere. Now the deck saves without issue and I can no longer reproduce this part of the issue.
However, in the Decklist-Tab, the problem mentioned in OP persists, i.e. the system thinks the card would require four copies of the style crafted in order to use it, when in reality even the base style would only require one copy to be crafted.
Further, the deck checker always expects four copies to be crafted, even for singleton deck lists, which should not be the case under any circumstances, so I would assume the wrong piece of code is called here.