Ok, it has nothing to do with sdl_mixer. It happens, when a timer must be initialized.

Code:
program sdlfpc;
{$IFNDEF FPC}
  {$APPTYPE CONSOLE}
{$ENDIF}

uses SDL;

begin
  WriteLn('Init Timer');
  if &#40;SDL_Init&#40;SDL_INIT_TIMER&#41; < 0&#41; then begin
    WriteLn&#40;SDL_GetError&#40;&#41;&#41;;
  end;
    
  WriteLn&#40;'SDL_INIT_TIMER Done'&#41;;
  SDL_QUIT;
end.
This code crashed too.

Cheers,
Thomas