An application developer may use the WM_HINTS window property to specify an initial state for a top-level window (either normal, iconic, or withdrawn state.) Window Managers are supposed to honor the initial state when the window is mapped for the first time. 

Running the test case (provided below) on Metacity 2.8.1 (GNOME 2.6.1) and Kwin 3.0 (KDE 3.4.0b) does not introduce any problems. However, when the test is ran on Metacity 2.16.1 (GNOME 2.16.1), the window is not in iconic state but rather in normal state when it's first shown. Using xprop one may make sure that the initial iconic state is correctly set in the WM_HINTS property, but the window changes its state to NormalState when it gets mapped.

The test code:

#include <X11/X.h>
#include <X11/Xlib.h>
#include <X11/Xos.h>
#include <X11/Xutil.h>

#include <stdio.h>

Display *display;
int screen_num;
Window root;

Window create_window(char * name, int x, int y, int width, int height) 
{
    XSizeHints sh;
    XWMHints wmh;
    Window win = XCreateSimpleWindow(display, root, x, y, width, height,
                                     2, // border width
                              BlackPixel(display, screen_num),
                              WhitePixel(display, screen_num));                 
    XStoreName(display, win, name);
    XSelectInput(display, win, ButtonPressMask | KeyPressMask);
    
    sh.width = width;
    sh.height = height;
    sh.x = x;
    sh.y = y;
    sh.flags = USPosition | USSize;
    XSetWMNormalHints(display, win, &sh);


    wmh.initial_state = IconicState;
    wmh.flags = StateHint;
    XSetWMHints(display, win, &wmh);

    return win;
}

int main(int argc, char **argv)
{
  Window f1;
  XEvent ev;
  XButtonEvent bev;

  int i, k;

  char *display_name = NULL;
  if ((display = XOpenDisplay(display_name)) == NULL)
  {
    fprintf(stderr, "Couldn't open %s\n", XDisplayName(display_name));
    return -1;
  }
  screen_num = DefaultScreen(display);
  root = RootWindow(display, screen_num);

  f1 = create_window("Frame 1", 100, 100, 200, 200);
  XMapWindow(display, f1);

  XFlush(display);
  XSync(display, False);

  while (1)
  {
    XNextEvent(display, &ev);
    if (ev.type == ButtonPress)
    {
      fprintf(stderr, "Hello, world!\n");
      exit(0);
    }
  }
}