Sometimes, after such jump, I start uncontrollably moving in one direction, usually straight into water and eventually off screen. The result was wiped save slot for beta. 2.53.
Did ZC crash, that wiped the .sav slot? What events transpired that led to a Game->Save?!
What ZC Player version did you use Alucard? 2.50.2? 2.53.0R2? Some 2.53.1 Beta? A 2.55. Alpha?
This will help not only Gégé, but will also determine if we broke anything in any of those newer builds that affects this, that we can fi internally.
P.S. Flip-screen is likely not in the cars, here. That would require a massive game rewrite, and I'm unsure why you would want it, as the entire point of this quest is Z3 scrolling.
The other issues, can surely be addressed. If Gégé moves this to 2.55 at some point, he can use the new F slot for a save menu that can be use anywhere. Even in 2,50., this is easy, but you have more options (an save types) in the new player.
Similarly, things such as his subscreen code can be made more portable, and other things cleaned up, but that is his option.
It is wondourful to see this quest progress to a Beta stage. It would be equally lovely to test it in 2.53.1, Beta 51+, and in 2.5.0 Alpha 73+ to rule out player issues.