Hi!

This is a really fun ask, I love me some wandlore! That and one of my favorite pastimes is solving JKR magical plot holes by figuring out the magical theory she didn't think all the way through.

So, the first thing I did was compare the two scenes you mentioned. This is the one from book 5:

“I have nothing more to say to you, Potter,” he said quietly. “You have irked me too often, for too long. AVADA KEDAVRA!” Harry had not even opened his mouth to resist. His mind was blank, his wand pointing uselessly at the floor.

(OotP, 813)

This is the one from book 7:

It was over: He could not see or hear where Voldemort was; he glimpsed another Death Eater swooping out of the way and heard, “Avada—” As the pain from Harry’s scar forced his eyes shut, his wand acted of its own accord. He felt it drag his hand around like some great magnet, saw a spurt of golden fire through his half-closed eyelids, heard a crack and a scream of fury. the remaining Death Eater yelled; Voldemort screamed, “No!”

(DH, 58)

Now, honestly, you're right, if the magic imbued Harry's wand in the graveyard I'd expect it to react to the killing curse Voldemort casts in book 5 the same as it did in book 7. And clearly, it does not. Even when it's the same situation, same spell, same enemy, Harry can't defend himself (if for different reasons). In both, his wand isn't even aimed at Voldemort at first at all.

So, I started wondering what is different between the scenes. Clearly, the situation is almost identical, so what difference could affect how Harry's wand reacts?

And then it hit me: Voldemort's wand.

In the first scene, in book 5, Voldemort is using his own wand, yaw and phoenix feather, brother wand to Harry. In the scene in book 7, the wand Voldemort uses is Lucius'.

So, my theory is that Harry's wand reacted differently because Voldemort wasn't carrying its brother, but a different wand.

So, with this in mind, let's try to explain what Harry's wand is doing and why.

The explanation we get in the books is that the Piori Incantatum in the graveyard essentially "charged" Harry's wand against Voldemort specifically:

“I believe that your wand imbibed some of the power and qualities of Voldemort’s wand that night, which is to say that it contained a little of Voldemort himself. So your wand recognized him when he pursued you, recognized a man who was both kin and mortal enemy, and it regurgitated some of his own magic against him, magic much more powerful than anything Lucius’s wand had ever performed. Your wand now contained the power of your enormous courage and of Voldemort’s own deadly skill: What chance did that poor stick of Lucius Malfoy’s stand?”

(DH, 600)

But I already mentioned here, that I don't think this scene is the real Dumbledore. So, I'm not sure how much faith can be placed in this explanation, especially since when Voldemort carried the brother wand, Harry's wand didn't shoot out golden flames.

(As an aside, I don't think wands can sponge up magic like that at all...)

But I think Harry's subconscious is right about the flames resulting from the multitude of magical connections between Voldemort and Harry. After the graveyard, they are, like, crazy magically connected. We've got:

Soul - Harry has a piece of Voldy's soul because he's a Horcrux

Blood (spirit) - Voldemort used Harry's blood in his resurrection ritual so their lives are bound to each other.

Magic - wands share a core.

And I'm going to forgo talking about the prophecy for this, but it's kind of bonkers how many layers of magic are binding them. And I think this is the key to it all.

So, essentially you have two wizards, that for the intent and purposes of magic, are as close as kin as possible. By soul and spirit, they are an extension of each other. So certain magic (like Lily's blood protection that is based on blood) probably sees Voldemort as an extension of Harry or vice versa. But they are not the same, as Dumbledore said in OotP: "but in essence divided", and other magic can recognize that (like the Elder Wand).

And the wands know this. Voldemort's yaw wand and Harry's holly wand are referred to as brothers, and I think that name is quite telling. Brother wands don't seem to want to fight each other, they share a core so they aren't meant to turn on each other, they are kin, extensions of each other. This is why the Priori Incantatum happened in the graveyard — to stop them from fighting. And if Harry cast a spell in the ministry in OotP, it would've happened again.

I think that first Priori Incantatum did change something and mattered for what happened in book 7. It basically was like an introduction. Afterwards, Harry's wand can recognize Voldemort, his magic, and his wand.

What I think happened with Lucius' wand is not far from Harry's subconscious explanation. The wand recognized Voldemort as Harry's kin, an extension of Harry himself, but he was carrying an unfamiliar wand - an enemy wand. I think the combination of kin with an unfamiliar wand is what caused it. Kind of like a jealous sort of "Harry isn't supposed to be with another wand". The yaw wand was fine because it shared the same core, the wands are connected just like Voldemort and Harry, so the brother wand wouldn't register as a threat.

For the holly wand, being attacked by an extension of Harry with an unfamiliar wand, felt off. Wrong. The magic felt wrong like it was 3 inches too far to the left. And I think that's what it reacted to. To the sense of wrongness that comes with seeing a familiar person somewhere, they really shouldn't be. This whiplash, I think, is what registered as a threat to the holly wand.

We know some wands can be sentient to this degree. Sycamore wands, burst into flames when they get 'bored':

It is a quirk of these handsome wands that they may combust if allowed to become ‘bored’, and many witches and wizards, settling down into middle age, are disconcerted to find their trusty wand bursting into flame in their hand as they ask it, one more time, to fetch their slippers. 

(from Pottermore)

Hazel wands die with their masters:

so devoted to its owner that it often ‘wilts’ (which is to say, it expels all its magic and refuses to perform, often necessitating the extraction of the core and its insertion into another casing, if the wand is still required) at the end of its master’s life

(from Pottermore)

So I think it's completely in line with what we know about wands that Harry's wand would get protective when something in Voldemort's magic feels off due to the unfamiliar wand. On the same page about wand woods holly wands are said to be very volatile and protective, so the behavior fits its personality. I think Harry's wand is protective of him and acts up to protect him when it recognizes it needs to. Voldemort and Harry's connection along with Voldemort using a different wand registered to the holly wand as a threat it needs to protect against.

TL;DR

Harry's wand recognized Voldemort as a kin of Harry. Voldemort's wand is its own kin, and therefore not a threat in OotP. The moment Voldemort, whom Harry's wand now recognizes, used an unfamiliar wand (Lucius' wand) Harry's wand registered him and the unfamiliar wand as a threat and reacted to protect Harry. The magic flames shot out were its own, not Voldemort's sponged-up magic.

12 for Harry: what do I think this character is up to post-canon?

Post CC Harry I hope is connecting with albus more and, if they have it, going to wizard therapy lol.

However, if disregarding cc and the epilogue and going from directly postwar, then harry is helping round up death eaters, both because harry wants other people to be safe but also because he isn't entirely sure who he is without Voldemort and being the chosen one. fingers crossed he'll figure it out, go traveling for a bit, quit being an auror and go teach defence at hogwarts.

7 on harry here

12 for Lucius: rotting away in the manor, being hated by both the death eaters and the light side, regretting re-joining Voldemort, not because he particularly gives a toss about muggleborns but because of what voldemort and war did to his family. his only confidants, other than his wife and son, are the peacocks.

7 for Lucius: what is my unpopular opinion on this character?

LUCIUS LOVES HIS WIFE AND SON MORE THAN ANYTHING! ESPECIALLY DRACO! (and draco loves him right back)

This is def more common with people who have only seen the films, but a lot of people act as if Lucius was abusive towards him but he was not! Lucius loves Draco so much he gives him everything he wants and spoils him rotten, and in turn Draco idolises him almost to the point of hero-worshipping him. He buys the whole Slytherin quidditch team new brooms, he tries to get the hippogriff that attacked him put down (sidenote: that wasn't rly dracos fault but thats another post), he gets them seats in the ministers box for the quidditch world cup. I don't think he was necessarily a good parent - Lucius allowed Draco to be a bully and he groomed Draco into idolising a violent murdering purist cult, then got himself thrown in prison and couldn't protect Draco from his own naivety when it was his turn to join. (And Voldemort saw how much Lucius loved his precious son and set him up with a suicide mission as punishment).

Draco wanted to be a Death Eater yes, both because he was a blood purist who had no idea of real violence and because he wanted revenge for Lucius' imprisonment. There's a bit near the end of ootp where Draco confronts Harry on getting Lucius arrested, Harry is in full idgaf mode but Draco, instead of formally calling him Father he calls him Dad and I love that bit (forever questioning why draco was essentially an extra in that film) because it shows them more intimately.

And during the battle of hogwarts, Lucius wants to call off the fighting to look for Draco. Lucius and Narcissa are running around through the fighting wandless and defenceless screaming for Draco, drawing attention to themselves, because they love him so much. And remember at this point the Malfoys are all completely fucked - they've got both the order and the death eaters gunning for them now.

Lucius also seems to be the most involved father of the series. James? Dead (rip). Arthur? Can't remember how many kids he has. Remus? Trying to abandon his wife and infant son. Hermione's dad? All I know is that he's a dentist. Seamus? Dad didn't even know his wife was a witch. You know fatherhood in the wizarding world is a sorry state when Lucius Malfoy comes out top.

20. Let’s admit, without apology, what we do to each other. (MCU, Thor/Loki)

“I should go,” Loki murmured, running his hands over Thor’s arm, though he made no attempt to leave. “It will be better, if I go.”

“Better for who?”

“For you, demonstrably. You’re king now. You have responsibilities and obligations and… stuff.”

“And stuff. Oh, that’s very eloquent. Didn’t we used to call you Silvertongue?”

Loki grinned. “You still do. You just did, in fact, not too long ago.” But his smile faded quickly. “I can’t be anything but a liability to you, and we both know it, so why not just admit it?”

“Better to admit what we do to each other,” Thor replied, pulling him even closer. “We’ve lost so much. Better to stop apologizing.”

“Better for who?”

I have such mixed feelings about Frigga, and this is actually kinda a perfect example of how a fan interpretation can differ (or even be incorrect) from what’s really happening on-screen, but that doesn’t mean the way the fan interacts with it has to change. 

In my case, I interpret and headcanon that Frigga and Loki’s bond is very strong and that Frigga only has his best interests at heart. I tend to write her that way as well, both when she appears in fic and when Loki is thinking about her. But, others have pointed out how Frigga’s treatment of Loki - while kinder than Odin’s - is just as manipulative and harmful, and the canon more or less supports that. I want to love Frigga and love her as a loving mom for Loki, but - well. 

In this instance, I don’t know why she would tell him not to make illusions. I mean, I can see it from an objective standpoint - she says that too many illusions will cause him to lose his grasp on reality, and certainly Loki’s grasp on reality is tenuous to start with (insofar as his own breakdown/mind torture is concerned) and she doesn’t want it to slip further. She wants Loki grounded in the “here and now,” - and, okay, that’s fair. 

But as you said, it begs the question of what, exactly, Loki should be doing instead. What good is being grounded or confronting reality if all he’s confronting is that he’s lost everything and has been imprisoned for life, with no one on the outside - save Frigga - who even cares. Loki’s reality is no picnic, and solitary confinement is mentally traumatizing; people lose their grasp on reality anyway, if they’re locked away for long enough. 

If recognizing that there’s nothing in his life worth dealing with and indulging himself in rewriting his own story to where he is the hero - but, more importantly, that his people love him - helps him pass the time (and “doesn’t make [him] feel any worse”), then by all means, why shouldn’t he indulge? 

That Frigga discourages him from doing this is a little side-eye-y, then, because - I don’t know, I would wager that she doesn’t want him to do this not because it’s harmful to him but, rather, because it makes her uncomfortable in some way. Maybe Loki playing out his own ideal story forces her to consider her role in how it all went wrong (lying by omission is lying, and she’s never stood up to Odin in defense of Loki that we’ve seen on-screen [although it’s implied she advocated for him to not be executed so, yknow, thanks for that]) and how much responsibility she holds for where Loki has ended up. 

Another aspect to consider is that her definition of reality might differ from Loki’s, in that she continues to refer to Odin as Loki’s father and when he finally snaps and says Odin is not, she counters with, “Then am I not your mother?” There’s this kind of implication that wanting Loki to “not lose his grasp on what’s real” includes wanting - or needing - him to continue to grasp the narrative of his life and of his family (that is, that he’s a member of this family and his parents are still his parents). Loki’s refusal to do so causes her to keep coming up against a wall with him, where they won’t see eye-to-eye. She doesn’t accept that she’s the one who needs to shift her perspective of the situation if she wants to get anywhere with Loki. 

I ... don’t know if I’m making sense. This could slip into a whole argument about how the core of Frigga discouraging Loki’s illusions while still insisting he’s their son is really about her wanting to control how Loki thinks and feels, and if that is what she wants, it says nothing too flattering about her as a mother. But I think that’s a topic that others can (and have) explored much more eloquently than I can, lmao.