Framerate drops, tearing appears when making SDL window resizable - c

Question

I just moved from SDL 1.2 to SDL 2.0 and I initially enjoyed similar performance (65+ FPS), then added Vsync in the renderer options and enjoyed a smooth 60 FPS with no tearing, then I added the flag SDL_WINDOW_RESIZABLE and the framerate dropped a lot (40 FPS without Vsync, 30 FPS with) and tearing appeared even with Vsync and side-scrolling became quite jittery. Whether or not I do anything to handle the resize event doesn't change anything. What am I doing wrong?
I'm using SDL 2.0.3 on VS2010 compiling in 64 bits. Here's the relevant code:
// This creates the window and everything associated with it
void graphics_init(srgb_t **sfb)
{
static int init=1;
if (init)
{
init = 0;
SDL_Init(SDL_INIT_TIMER | SDL_INIT_VIDEO | SDL_INIT_AUDIO);
}
window = SDL_CreateWindow ( VERSION, // window title
SDL_WINDOWPOS_UNDEFINED, // initial x position
SDL_WINDOWPOS_UNDEFINED, // initial y position
0, // width, in pixels
0, // height, in pixels
SDL_WINDOW_RESIZABLE | SDL_WINDOW_MAXIMIZED); // flags
SDL_GetWindowSize(window, &kW, &kH);
if (window == NULL)
{
fprintf(stderr, "Could not create window: %s\n", SDL_GetError());
exit(EXIT_FAILURE);
}
renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_PRESENTVSYNC);
texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_ARGB8888, SDL_TEXTUREACCESS_STREAMING, kW, kH);
*sfb = calloc (kW*kH, sizeof(srgb_t));
}
int main()
{
graphics_init(&sfb);
while (exit_flag==0)
{
... // main loop stuff that fills my buffer sfb
// Blits sfb buffer to screen
SDL_UpdateTexture(texture, NULL, sfb, kW * sizeof(srgb_t));
SDL_RenderClear(renderer);
SDL_RenderCopy(renderer, texture, NULL, NULL);
SDL_RenderPresent(renderer);
}
SDL_DestroyTexture(texture);
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
return 0;
}