In 2e, if I recall, there was a rule that a player couldn't cast both divine magic and arcane magic. 3e seems to seperate this into magic and miracles instead of two different types of magic, although the flavor text in the books discusses if they MIGHT theoretically be the same thing. But I didn't see a hard-and-fast "apprentices can't become initiates" rule, or one that would keep initiates from becoming wizards.
So in WFRP3, can an apprentice wizard go on to become an initiate and cast miracles in addition to his arcane spells, since one uses Favor and the other Power, and one uses Piety and the other Spellcraft? Since there's overlap on WP, that would seem like a scary character.