Really only the one. Not so convoluted as the previous linking. And not quite as wacky as my theory that Martha Liberty is Harry's grandmother. (Also, pretty sure Jim has said something that makes me just flat out wrong on that one, but I live in the tiny sliver of possibility here!)
I'm right in the middle of the battle at the end of Changes. The Grey Council has shown up and is kicking ass. And in the middle of it all, Harry hears someone further up on the pyramid using 'fuego' and feels sort of upset that 'someone was fuego-ing and it wasn't me'. Now, I haven't finished the reread, so maybe this is all nothing. But who was using Harry's spell?
IIRC, each wizard chooses their own 'made up' or ancient language to cast the spells in. Something that they don't actually understand so that they can assign value to the terms and add an extra layer of insulation between their minds and the stress of the spellcasting. So far, I believe that each wizard we've seen has their own spell language. Yes, they can cast other peoples' spells, but they tend not to. And if they do they tend to cast the spell using their own spell language. So who the hell was using Harry's fire spell?
Wacky theory of the day: It was Harry from the future.
We know that, at some point, Harry will break each Law of Magic. No time travel is on there. Don't ask me how or why, but I think future!Harry Showed Up too.
Of course, if I keep reading and it gets explained, then that's all out the window. We'll fuego that bridge when I get there.