Spring Data fills @LastModifiedDate by not @CreatedDate

I have following Spring Boot sample application. The crazy thing is if I add @EnableMongoAuditing annotation on SampleApplication bean, lastModifiedDate would be filled by createDate would not. Why is that? I searched the web and many people had problems on emptying createDate during an update, but I don't have an update.

Document class:

@Document
public class SampleBean implements Persistable<String> {

    @Id
    public String id;
    @CreatedDate
    public LocalDateTime createDate;
    @LastModifiedDate
    public LocalDateTime lastModifiedDate;

    public String name;

    @Override
    public String getId() {
        return id;
    }

    @Override
    public boolean isNew() {
        return id != null;
    }
}

Repository Interface:

@Repository
public interface SampleBeanRepository extends MongoRepository<SampleBean, String> {
}

Rest Controller:

@RestController
public class WebService {

    @Autowired
    private SampleBeanRepository repository;

    @RequestMapping("/insert")
    public String insert() {
        SampleBean sampleBean = new SampleBean();
        sampleBean.name = "Prefix" + new Random().nextInt(1000);
        repository.insert(sampleBean);
        return "done";
    }

    @RequestMapping("/")
    public Collection<SampleBean> home() {
        return repository.findAll();
    }

}

Application Config:

@SpringBootApplication
@EnableMongoAuditing
public class ApplicationConfig {

    public static void main(String[] args) {
        SpringApplication.run(ApplicationConfig.class, args);
    }
}