I seem to lose winter coins when buying the 40 coin-pack and get combo sledge and mittens. That should not be possible, as sledge is prized 19 coins and mittens 22 at the moment. I should get +1 on that combo. Instead I get -1.
The prizes you see are the amounts of wintercoins you have to pay if you buy items.
When you are selling items you get the amount of wintercoins minus 1 for every item.
At the first WinterEvent 2 years ago the prizes were the same for buying and selling items. But there was a lot of abuse (from RNs point of view, not ours!) so they changed that before the second WinterEvent started last year.