System Information:
Client Version: 2.11.0 ()
Client Operating System: Ubuntu 25.10
Build Architecture: 64-bit
Qt Version: 6.9.2

The Deck Format Legality checker is an extremely useful feature added in beta 39. As far as I can tell, it handles most cards perfectly, even cards that you can add an unlimited number of copies of to a deck, like Persistent Petitioners.

However, cards with a copy limit that is higher than 4, but not unlimited (e.g. Seven Dwarves and Nazgûl) get flagged as illegal if you put between 5 and their max number of allowed copies in a deck.

Steps to reproduce:

• Make a new deck and set a format
• Add between 5 and 7 copies of Seven Dwarves or between 5 and 9 copies of Nasgûl
• Observe the legality