The issue is caused by the property-ref attribute. Lazy loading only works when the many-to-one reference is using the other object's primary key since NHibernate assumes there's a foreign key constraint enforcing the validity of such a value. With a non-primary key (indicated by the property-ref), NHibernate does not make this assumption and thus does not assume the related object must exist. Since it does not want to create a proxy for an object that does not exist (i.e. should be null instead of a proxy), it eagerly fetches the remote object. This same issue exists when not-found="ignore" is specified since this indicates that the foreign key relationship is not enforced and may result in a null reference.