I agree. That's because I don't know the mechanisms of the game that I came asking here (I think most people do understand here). I think that if we can get over this problem, it could be helpful to a lot of people becaue I'm certainly not the first to get it. By the way, I've been in the 2nd false Sinnoh two times (seeking for its false Newmoon island):
The first time, I got there and I could not save because the game believed that I was in the Pal Park, where you cannot save until you get out. I've noticed that riding in the Mystery Zone was like flying over all the game maps but without any collisions anywhere. I ever got in front of Cynthia three times, like if I'd finished the Elite 4, just because I happened to pass just right there. I also ever got to be halted by the waiter in the Seven Stars retaurent (it was closed) and there it transported me in Grand Lake, just in front of the restaurent. I think that I passed over a Pal Park area.
The second time I reached the second false Sinnoh, I tryed to avoid the Pal Park invisible location by riding at the left of the first false Sinnoh. It worked, therefore it was all white. I explored around this gigantic spot of white to finally regornize some Calanave sprites. I then was able to get to Newmoon island (the music was Jubilife's, which means that I whould have gotten to the true place).
I was at the good spot to get to the true one, however I think that the problem is that it was all white. I think that this is what have done that to my save. Normally, it should be booting whith background all black, which can be taken away by displaying the Pokédex (or any other screen). I then should be on the same very spot and in the true Sinnoh.
This is how I understand the problem.