Jason busts through the window (sans cloth sack) and grabs Paul as the shot turns slo-mo. It then fades to a shot of Ginny being led away by paramedics, as she whimpers, "Paul? Paul?" I always thought that was a bit of a let-down.
Still, part three had an even lamer ending. Chris (the heroine) is in the middle of the lake when Jason's decapitated mother suddenly pops out of the water with her head re-attached! How's that happen?
Also, at the beginning of part two, Alice opens the refrigerator to find a severed head on the shelf. Whose head is it? I don't think it's Mrs. Voorhees, because we see her head on the shrine later, and it's in a much further state of decomposition.
Most likely there isn't an explanation as far as being apart of a script or anything. Most likely the creators of the film were'nt worried about making a continuity error, they just wanted to change the look, go a different angle, have a fresh look, you know the bullshit I'm talking about. In part 3 his noticeable changes are that of course he's now bald, alot bigger with make-up put on his neck and sholders to make him look stronger and of course in this film is where he first has his trademark hockey mask. Small bit of trivia: Sean Cunningham did not create the look of the Jason we now know and was in fact stated while producing one of the films that he didn't like the mask, it wasn't his creation and that he wanted it out of here. Sad and strange because we all very much like the look of Jason. I personally liked the way he looked in Freddy Vs Jason the best.