I've noticed that in Stackz! 7 Beta 4 the number of "cards left" does not count the card you're currently viewing. Thus, when you have the last card in front of you, it says "0 cards left"
This is different from the Stackz! I used until now (2005 v3), which does count the current card as a "card left". Then, when I had the last card in front of me, it said "1 card left".
Perhaps it's a bug, or perhaps it's just a philosophical change.
There were inconsitencies between learn and test dialogs. Now it shows you how many cards are left (the invisible ones). I think that's more natural, you don't have to be informed about the displayed card because you can see that. ;)