i've an hotkey in my app to switch bettewen fullscreen/windowed mode.
the first time i use it, i have to press twice the mod key (here shift) to activate it and when swithing is done to repress the mod key like state are lost when switching ...

testcase :
#include <SDL/SDL.h>

#include <iostream>

int main (int argc, char **argv) {
	SDL_Init (SDL_INIT_VIDEO);

	SDL_SetVideoMode (1024, 768, 0, SDL_FULLSCREEN);
	SDL_WM_SetCaption ("sdl_bug", "sdl_bug");

	int done = 0;
	bool f = true;
	while (!done) {
		SDL_Delay(10);

		SDL_Event event;
		while (SDL_PollEvent(&event)) {
			if (event.key.keysym.sym == SDLK_ESCAPE)
				done = 1;
			if (event.type ==SDL_KEYDOWN and event.key.keysym.sym == SDLK_f and event.key.keysym.mod&KMOD_SHIFT) {
				int flag = 0;
				if (f)
					flag &= ~SDL_FULLSCREEN;
				else
					flag |= SDL_FULLSCREEN;
				f = !f;
				SDL_SetVideoMode (1024, 768, 0, flag);
			}
		}
	}

	SDL_Quit();
	return 0;
}