The normal way to reparent (ie change the owner) of a widget should be to use the function:
void gtk_widget_reparent (GtkWidget *widget, GtkWidget *new_parent)
But this is only a "should be" since this function does not correctly do its job on some specific widgets. The main goal of gtk_widget_reparent() is to avoid unrealizing widget if both widget and new_parent are realized (in this case, widget->window is successfully reparented). The problem here is that some widgets in the GTK+ hierarchy have multiple attached X subwindows and this is notably the case for the GtkSpinButton widget. For those, gtk_widget_reparent() will fail by leaving an unrealized child window where it should not.
To avoid this problem, simply use the following code snippet:
gtk_widget_ref(widget); gtk_container_remove(GTK_CONTAINER(old_parent), widget); gtk_container_add(GTK_CONTAINER(new_parent), widget); gtk_widget_unref(widget);