I've encountered a weird bug. If you choose to surrender the map, it still "proceeds", despite the fact that you left (noises in the background). If you reenter the map afterwards, you can still see units from previous battle fighting.
zakia made a good point about the "weekly stereotypes". Once a card is in the challenge, it is used in 80% of the decks. You should win a random card in a weekly challenge.
I don't agree with the rest though. For me Kongai deserves 5/5:D