I have come across a bug in the very last scene, on the rooftop of the skyscraper when you play the piano and the girl is supposed to hold the stairs for you, in some instances she simply doesn't. I have played the game a second time and then she grabbed the thing as she's supposed to.
The only difference I can think of is that I in the game that bugged out I still have both decks of images for the projector, the magnifying-class and the missing tile in my inventory as I used the magnifying-glass on the butterfly to figure out the code for the door in the greenhouse.
Since the game locks you in the rooftop-room once you have the girl with you, I cant really do anything about it. I have tried everything and simply have to admit that this is a bug. It prevents me from finishing the game this second time around.
Please tell me what more information you need, can I provide you with a save-file for you to investigate which trigger is not set or something?
Well she won't hold the switch on her own, you must click it once you play the melody.