Here is a simple test which creates/maps a windows at location (100,100) and on 
mouse press move the window at the same location.
Under Metacity everything works fine (second move does nothing), however under Compiz we have a different story :(
initially it places so decoration would placed at (100,100) and the window itself has different coordinates ((104, 124) in my case.
But after XMoveWindow() it moves the window at (100,100), so decorations are
at (96, 76).

I may be wrong, but my interpretation of ICCM (http://tronche.com/gui/x/icccm/sec-4.html#s-4.1.5) is that WM should treat
coordinates from XMoveWindow() the same way as from hints for initial showing. 

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

#include <stdio.h>

Display *display;
Window root, w1;

Window create_window(char *name, Window parent, int x, int y, int width, int height)
{
    Window win = XCreateSimpleWindow(display, parent, x, y, width, height,
                                     2,
                                     BlackPixel(display, 0),
                                     WhitePixel(display, 0));

    XStoreName(display, win, name);

    XSizeHints *hints = XAllocSizeHints();
    hints->width = width;
    hints->height = height;
    hints->x = x;
    hints->y = y;
    hints->win_gravity = 1 /*NorthWest*/;

    hints->flags = PPosition | USPosition | PSize | PWinGravity;

    XSetWMNormalHints(display, win, hints);
    XFree(hints);

    return win;
}

int main(int argc, char **argv)
{
    XEvent ev;
    char *display_name = NULL;
    if ((display = XOpenDisplay(display_name)) == NULL)
    {
        fprintf(stderr, "Couldn't open %s\n", XDisplayName(display_name));
        return -1;
    }

    root = RootWindow(display, 0);

    w1 = create_window("Window", root, 100, 100, 100, 100);
    XSelectInput(display, w1, StructureNotifyMask | ExposureMask | ButtonPressMask);

    XMapWindow(display, w1);

    XFlush(display);

    while (1)
    {
        XNextEvent(display, &ev);
        if (ConfigureNotify == ev.type) {
            XConfigureEvent e = ev.xconfigure;
            fprintf(stderr, "ConfigureNotify: w=%x, x=%d, y=%d, send=%d\n", e.window, e.x, e.y, e.send_event);
        } else if (ButtonPress == ev.type) {
            XMoveWindow(display, w1, 100, 100);
            fprintf(stderr, "button pressed\n");
        }

    }

    return 0;
}