Just added 10 new cards: seven are from 2016 and three from 2017. What can I say? Probably something is not working properly.
Before I bought anything I had 345 credits. Then I've bought 5 cards from 2016 and popup info shows up: "Cashback bonus! 30 credits added to your account". Wait... two things are strange:
1st: I've bought FIVE cards. Not TEN. Credits has been added to my account anyway.
2nd: It says "30 credits". Not 15 but 30! I'm double diamond, so my price is 15 credits per show. I've took calculator and check: 345 - 5*15 = 345 - 75 = 270. I should have 270 credits after five purchases, but system gave me 30 credits back, so now it was 300 :D.
OK, let's see what happens after another five cards. This time I selected one card from 2016, 3 cards from 2017 and another one from 2016. The same popup info. Another 5 cards purchased and another 30 credits back. The same math: 300 - 5*15 = 300 - 75 = 225. I should have 225 credits, but system gave me another 30, so now I have 255 credits.
Summary:
10 cards should cost me: 10*15 = 150 credits.
Rules of this offer says "buy 10 cards and last two of them will be refunded", so I should get back 2*15 = 30 credits after 10 purchases.
In fact I got back 30 credits after every 5 purchases, so 2*30 = 60 credits after 10 purchases.
10 cards in price of six. 4 cards refunded - Now I like this offer :D.