what is HEADLESS ? (hint, that might be why isn't fixed)
What defines that ?
(is it something SDL does ? or your OS ?)

Headless means non Graphical Enviroment without Desktop, only Console uses SDL/FBcon automatically.

How to reproduce:
Install any minimal Linux OS Image without Desktop (Fedora,Debian)
install dosbox and type anything with "scancodes=true" most enabled in Basic Configuration. (For my Site keyboardlayout=de129)

Now as example Type "L" and see "A" was drawn in Dosbox.

I mean who defines HEADLESS ? (the variable in the !defined)
Where does it come from ?

Ah sorry i have copied the wrong file (own Workaround in Progress), i comment out this Lines for my Headless use.

SVN sdl_mapper.cpp:
#if !defined (WIN32) && !defined (MACOSX) && !defined(OS2)
/* Linux adds 8 to all scancodes */
else key-=8;
#endif

I need something to detect in order to disable it.

Possibly check used SDL_VIDEODRIVER is not X11..

you mean the environment one ? I don't think that one is set by default. The user can set it to override things.

Oh. Find another one. Not tested with svga and directfb.. XVFB same problem.

1static char driver[16] = { 0 };
2	SDL_VideoDriverName(driver, sizeof(driver));
3	if (::strcmp(driver, "x11") != 0)

EDIT: i have read Informations, its a X11 Problem.. Wayland not adds 8 on Scancodes.