Morally yes, but they don't have a value unless activated (I think this is stated on the card?), so hopefully not. I plan to start hoarding these, and others, for future promos. If you can't beat 'em.....
This was my take too. Annoyed when they told me what had occurred though. They told me they were going to refuse to activate the cards when brought back in but not sure how that could be done. Anyway, like you I will hoard some for next time.