title: GtkDialog mapped without a transient parent
body: <p>I have a GUI built in Glade (3.18) which is called by a Python 3 program (using PyGObject). I get a lot of warnings when running the program (Fedora 21) that say:</p>
  
  <pre><code>Gtk-Message: GtkDialog mapped without a transient parent. This is discouraged.
  </code></pre>
  
  <p>How can I fix this warning? I tried filling in the field <code>Transient for: main_window</code> in Glade for all the dialog windows, but the warnings still appear.</p>