LOL I have noticed this too. I guess I assumed that the photos were two to a prize box, since sometimes it would add up to being that (4 pics, 3 prizes and 5 prize boxes to unlock). However, that's not always been the case. I'm sure they just didn't update something in the code when they added buddies and such, like Monty said.
Who knows, but I don't mind getting extras.
~Vicks