"It's Always Sunny In Philadelphia"? I'm pretty sure that's inaccurate. Someone's told you a weather-lie, and I'm not even sure why you'd bring it up just now.
(For anyone confused, panel four visually references a moment from that show that I am mostly aware of due to it having become a meme.)
I wanted it to be extra clear that not every spell has been noticeably affected. That's not exactly the same as not having been affected at all, but a lot of spells, used without any attempt to modify them, will behave as they always have.
Of course, if one were to attempt to modify them, it's possible some things that weren't previously possible would be...
Anyway, that could be anyone with Rhoda's hairstyle. How dare you make assumptions.
Amanda is canon, and this will be far from the last we see of her.
How They Learn
Given the present situation, the answer to why this is happening isn't in any book, and could only ever be guessed at by the characters. Even if they sorted out all the technical details, there's no way to confirm on their own the why of this situation.
Given this, I basically had three options.
1 - Leave characters in the dark with their hypotheses, only reveal the truth via narration.
2 - It's a secret to everybody, not to be revealed even by narration.
3 - The heck with it, let's just have an established character tell Grace what happened.
Given that this wasn't written as some sort of philosophical thought puzzle in which the question is the entire point of it, I chose option three, and we shall soon know what excuse I came up with for this nonsense.
I'm sure someone somewhere will criticize option three with all of their fury, but at least I didn't go with secret hidden option four:
4 - Literally have The Will of Magic itself summon up the seers again and be like "whoops my bad here's the scoop my dudes."
And yes, The Will of Magic would have phrased it that way, for the quality of the dialogue would not have been allowed to rise above the quality of the scenario itself.