Problem with a video surface

hi all
i set a video surface like this…
screen = SDL_SetVideoMode(1024, 768, 32,SDL_HWSURFACE|SDL_FULLSCREEN|SDL_DOUBLEBUF|SDL_HWPALETTE);
why i have problem when i press alt-tab and the come back to the program in windows?
there is a solution? am i wrong?
thanks
Fede!