@Qube: you're right, there's something wrong with the demo.
I just improved my map_writer tool, and it supports Magic Pockets too.
I unpacked PC files using XFDDecrunch on amiga (was RNC format!!), and added an offset for tile index in the config file of my tool.
I have ripped the PCMAP.PAP map, which is the PC / NTSC first level and also the demo level. A funny thing is that LEVEL1B.PAP contains PAL level 3 of world 1 whereas it never appears in the PC / NTSC version (PAL level 1 shows up instead)
We don't need to rip the demo map, since it's 100% the same as the one attached => problem solved, thanks to the PC files & XFDDecrunch.