I've tried it multiple times, and can say with confidence that the feather required for the first Sphere of Knowledge test (Air mage walkthrough) does no give any XP. So it's impossible to complete the game with 500 XP playing as the Air mage. I've completed the game with every class and finished 500 XP walkthrough with Water Mage just yesterday. For every class except Air, the item required for the first Sphere of Knowledge test give 1 XP. I've also seen other people on Steam forum complaining about this issue.
Hope it'll get fixed, soon. Otherwise, I've experienced no issues with the game, it runs perfectly.
Hope it'll get fixed, soon. Otherwise, I've experienced no issues with the game, it runs perfectly.