I have a theory about Peter and why he can only sometimes fly. I think perhaps his power isn't that he can fly. Rather, he is able to absorb some of the powers of other heroes who are nearby-- kind of like a cheap Rogue knockoff. That would explain why he's only able to fly when he is near his brother, why he's able to move around during time freeze with Hiro, and why he had the same eyes as the painter guy in the preview.