OK, so I tested a deck in TG with at least one common, uncommon, rare and mythic that all had zero XP. Each card received 6 XP after the win. The XP bar shows different progress for each rarity, which seems correct. However, instead of the normal 5 wins for a common card in TG, it now seems it's a lot more.
@Brigby: a couple of questions: 1) Is it intentional that the number of wins required to master a card in a particular event has changed? 2) Where can we find a list of how much XP a card of a given rarity needs to be mastered?