While rewriting the music, I realised that music plays faster at 60 Hz (well, no surprise at all... it is the standard behaviour of any MSX game whose background music is synced to the VBLANK interrupt).

But, in this case, I think the 60Hz music differs too much from the original C64 one, and, for the first time, I don't like it. So, I felt that the game needed an option to play @50Hz on 60Hz MSX2 machines.

I've done it the easy way: press F1 during the game startup and it will switch to PAL mode so you can enjoy the music at a tempo that is closer to the original Rob Hubbard's composition.