The Cold Shoulder
Dumbledore has always been Harry's wizard mentor. The headmaster of Hogwarts has been there to help our favorite boy wizard with all his most pressing problems. (Except that whole being illegally entered into the Tri-wizard Tournament business…but we digress.)
This year, Dumbledore takes a different route—he totally and completely ignores Harry.
Sure, Dumbledore shows up to defend Harry during his trial in front of the Wizengamot, but then he won't even speak to Harry afterwards. Then, he avoids Harry all year at Hogwarts. That's probably why, when Hermione encourages Harry to tell Dumbledore that Umbridge is forcing him to write lines in his own blood during detention, Harry blows her off. Dumbledore won't even look at Harry. What's he gonna do to stop Umbridge?
To make matters worse, Dumbledore never explains why Harry keeps having those weird dreams about the black hallway and Voldemort's snake. He just assigns him special Occlumency lessons with Professor Snape—which almost makes detention with Dolores seem like a picnic.
Of course, by the end of the movie, Dumbledore has shown up to battle Voldemort and save Harry. That's pretty swell of him—but what was the whole cold shoulder routine about?
He also finally reveals some key info to Harry in one of their patented end-of-the-school-year chats:
HARRY POTTER: The prophecy said neither one can live while the other one survives. It means one of us is going to have to kill the other, in the end.
HARRY POTTER: Why didn't you tell me?
DUMBLEDORE: For the same reason you tried to save Sirius. For the same reason your friends saved you. After all these years, after all you've suffered, I didn't want to cause you any more pain. I cared too much about you.
Yeah, so maybe Dumbledore did drop the ball this year with Harry, but it wasn't because he didn't care about the kid. In fact, just the opposite. He wanted to protect the boy. It's a goof up Dumbledore feels pretty awful about, too:
HARRY POTTER: It's my fault.
DUMBLEDORE: No, the fault is mine. I knew it was only a matter of time before Voldemort made the connection between you. I thought by distancing myself from you, as I have done all year he'd be less tempted, and therefore you might be more protected.
It's kind of true. Sure, Dumbledore was trying to protect Harry, but maybe if he'd been straight with him about what was going on, Harry wouldn't have gone running off to the Department of Mysteries and Sirius wouldn't be dead.
Dumbledore's remorse will set the stage for a whole new relationship between Harry and his headmaster in the next film. Maybe that means we'll finally figure out what the heck is going on around here.