Ok, there was no justification at all for that. Dumbledore has been blind before, but there's NO excuse for him to continue to inhibit Harry's learning after that performance.
All in all, it was an outstanding chapter. I didn't understand the "Ksilisab" thing until the second time it was brought up. Does Luna know what it is? Is she just teasing them, or did the word just...pop into her mind?
As great as Draco is in this story (and he really is), Harry is just too good for words. I can't wait for more.