Decks should "use" a card in my inventory.
For example, I own 8 Arid Mesa. If I load two decks into Deckbox that each use 4 Arid Mesa, when I load the third deck that uses X Arid Mesa, Deckbox shouldn't say "Oh, you own 8 Arid Mesa. I won't include these in the list of cards you don't own." If I need 12 Arid Mesa but only have 8, I should be able to see that somehow and specifically for the deck that requires them ("Oh, I'm short on that card. I should just grab my copies from deck X, where they currently reside.")
Thanks!
We totally need this. It would make managing your cards so much more easier and effective, even when you are not near your decks.