GdkWin32: Avoid ShowOwnedPopups in gdk_win32_window_hide
gdk_win32_window_hide() calls ShowOwnedPopups(hwnd, FALSE) and that hides all windows that are owned by hwnd.
If a GtkWindow has any other GtkWindow as transient children, the call to gtk_widget_hide() has the side effect of hiding also its transient children. Removing the call to ShowOwnedPopups(hwnd, FALSE) fixes this.
I have attached a test showing the issue. I suggest to test on X11 and then on Win32 and see the difference. With this patch applied they work the same