OK, I got a second report from Win 8.1 user about this. The game (SDL2 + OpenGL) is having trouble with the screen (fullscreen only), only part of it is visible. Running the game with administrator rights fixes the issue.

What's the problem? Any clues what's going on? Is this a know problem of SDL?

I don't use anything fancy in my code, just the standard SDL libs, ancient OpenGL without any shaders and nothing more. Nothing really that could be suspected of causing this...