I read this as meaning that Dumbledore's order that Snape stop reading minds is just to mollify Harry. Dumbledore reads students' minds (I argue here that Dumbledore reads the Weasley twins' minds), and hence doesn't actually care whether Snape does the same.
Harry, of course, has no way of checking that Snape is following this order, so it's safe for Dumbledore to cross his fingers under the table, so to speak.
Dumbledore never promised to stop reading student's minds. Not int chapter 18 when he said Snape would make that promise or in chapter 20 when he is called on reading HJPEV's mind.
Also, Dumbledore's offered compromise to HJPEV was this:
He will promise to only read minds when the safety of a student requires it.
It is not difficult to argue that the safety of some student, somewhere requires constant readings of the minds of the Weasley twins.
EDIT: New discussion thread here.
This is a new thread to discuss Eliezer Yudkowsky's Harry Potter and the Methods of Rationality and anything related to it. With two chapters recently the previous thread has very quickly reached 500 comments. The latest chapter as of 17th March 2012 is Ch. 79.
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: one, two, three, four, five, six, seven, eight, nine, ten.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
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: