Ok so here is what I think now that I read it all and reconsidered:
1.4.7 introduced a massive change on Mastery ranks. Ranks were rebalanced and it was made easier and faster to reach consecutive ranks. Mastery earned in previous versions would stay and your Mastery rank would go up according to how much total Mastery you earned until the update.
However, a problem occurred. There were some (or let’s say, a lot of) players that had more total Mastery on one or more classes than the new maximum would have been (including my Wizard – all other classes of mine are below this new maximum)! This confused the game so much that it probably gave out a fatal error or something while applying the rebalancing during the first launch of the update (“Loading balancing into memory”), and the game would refuse to launch for anyone that had such a high-ranked class. Rovio got aware of this issue through many angry and sad complaints from players and had to find a quick solution.
As the solution, they presented 1.4.8: the rebalancing of Mastery ranks is still there, but instead of accrediting all earned Mastery, they only accredit so much Mastery that the user’s progress is exactly the same as before the update. Which means that all players – including the ones that didn’t originally have the problem! – lost a lot of total Mastery and wasted a lot of time grinding and spending Snouts at the Dojo, but at least, their way to the maximum rank is a bit shorter now.
Honestly, I think they could have accredited just so much Mastery that all birds beyond the maximum cap are capped off at the new maximum cap and stay as M15. That would have been the best solution for all. But maybe it would have taken too long for Rovio to code in. Or they had an interest in making players spend some more money even after the update.
EDIT: I do not understand, however, how an M9 class would go to M14 just from rebalancing. My Bard had 124,066 total mastery points before the update. That was enough for M9. This amount of Mastery is enough for M10 with the new absolute numbers. To M14, Bard is missing more than 100k Mastery points. She would have needed M11 on the old game if she was to obtain M14 on the new game.
