This has been going on at least since the new expansion released. Basically, if I copy a deck code from somewhere and use it to try and replace a current deck, it will not replace my deck with the new one. It appears to have done so by including all the cards from the new deck. However, if I re-open the deck or try to use it in constructed play it reverts to the old deck.
There are two workarounds I have used so far. The best one is to replace my old deck, close it, then immediately quit and re-open the game. The new deck will have properly replaced the old one. The other workaround is to replace about 3-5 cards in my deck, close it, then re-open and keep replacing cards. This is pretty inconsistent though, and old cards will often not be replaced at all. Both of these methods are tedious to do, obviously.
Any incoming fix would be appreciated.