use delay_trait_notifications in Configurable._load_config

IPython/config/configurable.py

@@ -138,11 +138,14 b' class Configurable(HasTraits):'
             section_names = self.section_names()
         
         my_config = self._find_my_config(cfg)
+        
+        # hold trait notifications until after all config has been loaded
+        with self.delay_trait_notifications():
         for name, config_value in iteritems(my_config):
             if name in traits:
                 if isinstance(config_value, LazyConfigValue):
                     # ConfigValue is a wrapper for using append / update on containers
-                    # without having to copy the 
+                        # without having to copy the initial value
                     initial = getattr(self, name)
                     config_value = config_value.get_value(initial)
                 # We have to do a deepcopy here if we don't deepcopy the entire