I bought the new Mastery Track from the Crystal Bloom vendor with two of the new currency (Crystal Bloom) in Eye of the North, but the Dragon Slayer mastery line didn't unlock.
Now the item is gone from both of the new vendors and I'm locked out of exp gain in story instances and missions.
Picture : You see that the track is still locked AND the mastery purchase gone all at once on the vendor.
Edit: Okay, never mind. The whole thing was unclear. You unlock the track from story progression: When you speak with Aurene after you return from Rata Sum. The item you buy at the NPC vendor is actually the second tier of said track. I don't know if the exp from the Rata Sum story istance was accounted for though.
Not sure whose's idea it was to allow the 2nd tier purchase before even unlocking the track or to award experience from a first story instance without the track being unlocked... The whole thing is backward.