Yeah, unfortunately that's a bug I do know about, but not sure how to fix it.
Generally, it shouldn't let you remove cards from your Deck if you don't have enough cards left. But there's a chance I missed some cards here and there.
Not sure if you've gotten around to it but the card that adds ultimate dark fairy queen to your deck/hand definately didn't force you to have a remaining deck of 5+ to remove 5 cards from it in the original demo.
