This is a fantastic demo!
On my Chrome browser, absolutely everything works as I would expect, except
(1) The very first click on a card does nothing — the card has a “hiccup”, but doesn’t turn over. Second click works to turn over.
(2) Repeat click on the card doesn’t turn it back over, which is at least intuitively what I would have expected. But maybe for Tarot purposes it should stay turned over?
At any rate, I hope you’ll continue to make the demo availiable at TiddlyHost, since I could imagine this becoming something like an edition, the “Tiddly Tarot edition” — where the cards could then take their positions within a reading layout or two, and someone would then add in a full suite of interpretive tiddlers, etc. Great proof of concept!
PS: I did get duplicate cards (within the same array) while playing with the tiddler called “Pick your cards (this will be saved)” — So the algorithm to remove cards from the deck once they’re face up (or to assign values earlier, at the point when they’re still face-down) needs tweaking. 