I thought I had the same problem yesterday when i bought 2 cards from the carousel for 4 credits instead for 2 credits. I dont know why, but I went to the Bugs & Fixes forum section and found out there is a new beta version released. One of the changes include "Cards in the carrousel are not discounted anymore." The old version of the software will keep saying the demo cards are for 1 credit so I'd suggest to install the new version to avoid *****. Hope I helped.