That's something in the original universe which seems unrealistic to me, so I guess it doesn't work exactly that way in MoR. Someone in the ministry being warned, with the details of the spell used, for every spell used around an underage would mean, de facto, being warned of almost every spell usage done by any parent. It would mean that every spell cast by Lucius when Draco is nearby is detected by the ministry. I doubt both the Death Eaters and the "normal" wizards would accept something like that.
Also, in canon Order of the Phoenix, near the end, Umbridge attempts to cast Crucio on Harry to make him talk, and when she does that, she hides the portrait of Fudge so Fudge doesn't know. If any spell cast near an underage wizard is detected by the ministry, they would know anyway about her casting of Crucio on Harry.
There are many other examples : like, at the end of the Goblet of Fire, Voldemort and his acolytes use many Unforgiveable curses around Harry (killing Diggory, torturing Harry, ...) and there isn't the slightest hint that the ministry detected all that.
So my guess is that the "trace" isn't a perfect detector of every magic used around an underage, but maybe just magic used around an underage by someone who isn't a grown up wizard ? It would detect underage magic, Dobby's magic usage around Harry, but not when parents cast spells around their children, nor when adults (mad Hogwarts teachers or Death Eaters) attack children ?
There is a simpler possibility.
The trace only detects the magic of the caster. The reason that Harry got the note for Dobby's use of magic is because Dobby used inscrutable house elf magic to fake Harry's magical signature.
Or, alternatively, they knew that tracking every spell everywhere there was a child would result in them being inundated with reports, be a violation of privacy, etc., so they have it set to disregard spells cast in known magical areas--basically allowing carte blanche for wizard-raised students, while completely shafting the muggle-rais...
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 90. The previous thread has passed 750 comments.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18,19.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: