using (TransactionScope scope = new TransactionScope())
{
    ISession session = sessionFactory.OpenSession();
    MappedEntity entity = new MappedEntity() { Name = "Entity", Value = 20 };
    session.Save(entity);

    entity.Value = 30;
    session.SaveOrUpdate(entity);

    // This returns one entity, when it should return none
    var list = session.
               CreateQuery("from MappedEntity where Value = 20").
               List<MappedEntity>();
}

using (TransactionScope scope = new TransactionScope())
using (ISession session = sessionFactory.OpenSession())
using (ITransaction transaction = session.BeginTransaction())
{
    //Do work here
    transaction.Commit();
    scope.Complete();
}