SDL_WINDOW_FULLSCREEN_DESKTOP on widescreen

Hi,
I have a question about how to use SDL_CreateWindow with SDL_WINDOW_FULLSCREEN_DESKTOP flag set.
My game has a resulution of 800x600 and i want to stretch it over the whole screen (Android / Linux).
I think i did something wrong. What I did is the following:

mWindow = SDL_CreateWindow("",
SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED,
0, 0,
SDL_WINDOW_FULLSCREEN_DESKTOP);

mRenderer = SDL_CreateRenderer(mWindow, -1, 0);

SDL_SetHint(SDL_HINT_RENDER_SCALE_QUALITY, "linear");
SDL_RenderSetLogicalSize(mRenderer, 800, 600);

This results in a unstretched result under linux (black borders) and android (blink borders). I have a FULL-HD 16:9 Display.

Have I missunderstand the SDL API or is it a bug?

Best regards,
Artem