Bellatrix was still transparent within the Cloak, but to Harry she was no longer hidden, he knew that she was there, as obvious to him as a Thestral. For Harry had only loaned his Cloak, not given it; and he had comprehended and mastered the Deathly Hallow that had been passed down through the Potter line.
Wow, how did I manage to miss this? When does that happen?
Chapter 56: