remove hack I did for #5366, It was most probably due to #5375. see #5366, #5375

src/message_window.py

@@ -764,9 +764,6 @@ class MessageWindow(object):
 			old_ctrl.set_control_active(False)
 
 		new_ctrl = self._widget_to_control(notebook.get_nth_page(page_num))
-		if not new_ctrl:
-			# This event is sometimes exposed without any reason. see #5366
-			return
 		new_ctrl.set_control_active(True)
 		self.show_title(control = new_ctrl)