Corrected entry: Just after Harry speaks to Sirius in the fireplace and Ron comes down, Ron leaves and Harry goes back to the fireplace. In the background you see Ron going up the stairs, he goes into the dormitory on the right, but this is the *Girls Dormitory*. When they all arrive in the Common Room in the first movie, Percy says, "Boys' dormitories is upstairs and down to your left. Girls' the same on your right. And also in the first film, we see Hermione go through the door on the right after they see Fluffy for the first time.
Jennifer 1
13th Mar 2009
Correction: This is four years later. It's entirely possible they switched the dormitories. Remember, it's a magical place so it wouldn't be difficult. Also, a number of things change physical locations between the films. For example, Hagrid's house and the Whomping Willow have been repositioned several times. There is no inconsistency within this film.
Yes, but why would they want to?
Same reason people in real life change where their own bedrooms are. They simply want a change as things can get dull keeping them the same all the time for many people.