NHibernate not evicting objects from a session

Assert.That(Session.Contains(_beveragesCategory), Is.False);
Assert.That(Session.Contains(_beerCategory), Is.False);
Assert.That(Session.Contains(_darkBeerCategory), Is.False);
Assert.That(Session.Contains(_lightBeerCategory), Is.False);

Assert.That(_beverageCategory.ChildCategories[0], Is.Not.SameAs(_beerCategory));

Assert.That(fromDB.ChildCategories[0], Is.Not.SameAs(_beerCategory));