Enabling dirty tracking by using the Bytecode Enhancement Maven plugin in combination with annotations @DynamicUpdate and @SelectBeforeUpdate attached to the corresponding entities ensure that partial updates are possible with Hibernate. But as soon as a javax.validation.spi.ValidationProvider like org.hibernate.validator.HibernateValidator is registered, the BeanValidationEventListener is validating all properties of the entity, even those that haven't been updated. So in fact, the partial update succeeds but the validation fails, if the developer doesn't set the mandatory fields annotated with @NotNull explicitly, although their annotation property @Column.updatable is set to false.
To fix this issue, I'm already preparing a pull request. As soon as this is done, I'll add a corresponding comment to reference it.
Java Persistence API 2.1 (1.0.2.Final)
Hibernate ORM (5.2.7.Final)
Hibernate Validator (6.0.13.Final)
Hibernate Enhance Maven Plugin (5.2.7.Final)