If Dumbledore had kept the Map himself - if the Weasleys had ever spoken of it to Dumbledore - but they did not, thankfully.
Calling out explicitly why this is confusing:
The trapdoor had hardly slammed shut above them before all nearby sounds muted and the old wizard spun on them and held out a hand and commanded, "Give me the map!"
"M-map?" said Fred or George in total shock. They'd never even suspected that Dumbledore suspected. "Why, w-we don't know what you're -"
"Hermione Granger is in trouble," said the old wizard.
"The Map is in our dorm," George or Fred said immediately. "Just give us a few minutes to get it and we'll -"
The wizard's arms swept them up as if they were hugging-pillows, there was a piercing cry and a flash of fire and then the three of them were in the third-year Gryffindor's boys' dorm.
The Weasleys quite definitely told the location of the map to a Phoenix wielding, sorting hat summoning, line of Merlin holding person who looks like Dumbledore. So either Quirrell is lying, or someone Obliviated the Weasleys before Quirrell stole the map from them. Further, Harry knows this.
If the enemy can notice you running off to consult the Weasley twins during class after Hermione was arrested, and find out about that magic map you said was stolen, then the enemy can wonder why I was guarding Hermione Granger's body.
By the way, that line was edited. It originally read:
If the enemy can notice you running off to consult the Weasley twins during class after Hermione was arrested, and find out about their magic map and steal it, then they can wonder why I was guarding Hermione Granger's body.
From discussion context, I believe the line was edited because it wasn't clear how Harry could have learned about the map on his own and people were theorizing that Harry stole it himself.
'it' in Quirrell's rant is the true name dealio, not the Maurauder's Map.
New long chapter! Since I expect its discussion to generate more than 160 comments (which would push the previous thread over the 500 comment limit) before the next chapter is posted, here is a new thread.
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 108
(and chapter 109, once it comes out on Monday).EDIT: There have now been two separate calls for having one thread per chapter, along with a poll in this thread. If the poll in this thread indicates a majority preference for one thread per chapter by Monday, I will edit this post to make it for chapter 108 only. In that case a new thread for chapter 109 should be posted by whoever gets a chance and wants to after the chapter is released.
EDIT 2: The poll indicates a large majority (currently 78%) in favor of one thread per chapter. This post has been edited accordingly.
There is 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.)
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: