It's Harry's curse, I guess that people can't see he isn't like his father. Snape has known him for 5 years now and still doesn't seem to have managed to catch on.

I don't know. Sirius and Harry still creeped me out. Harry was forced to become the adult in that situation and to feel like he had to protect and "save" Sirius from the moment he first met him. Harry created a perfect godfather to go with the perfect image of his dead father and all of that crumbled in OotP...