type system question

["CESAR MENA, BLOOMBERG/ NEW YORK" <CMENA bloomberg net>]

hello all -
could anybody explain why is it necessary to call
LOOKUP_TYPE_NODE after gtk_type_class_init, if if was already
called??  if the variable 'node' was already pointing
to the right place in the type_nodes list, why would
calling gtk_type_class_init change that?? 
please excuse my ignorance if this is a ridiculous question,
but i don't see the point.
many thanks  

gpointer
gtk_type_class (GtkType type)
{
  GtkTypeNode *node;
  
  LOOKUP_TYPE_NODE (node, type);
  g_return_val_if_fail (node != NULL, NULL);
  
  if (!node->klass)
    {
      type = node->type;
      gtk_type_class_init (type);
	/* i don't understand why this call is necessary */
      LOOKUP_TYPE_NODE (node, type);
    }
  
  return node->klass;
}