Yes, this is a little troublesome. But the major difference is of course that Voldemort is now back in his powers and can act on his knowledge in a way that was not open to him before.



Knowing that house, the doorbell probably has some sort of trap attached to it. I don't think Harry's yelling would have been loud enough to wake the portrait. They are perfectly able to whisper around it, and they can talk normally in all other rooms, so I think it only reacts to loud noise close to. All the examples of it waking up are noises that would start you awake, too. The twins would call his yelling loud if they could hear it at all, which they probably could.



Perhaps it is a safety mechanism built in precisely to keep people from using it to sneaking up on people?