JPA update query: cache not properly invalidated

Why doesn't it work:

@Test
public void test() {
    EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("test-pu");
    EntityManager entityManager = entityManagerFactory.createEntityManager();
    String id = "id";
    long value = 1234L;

    entityManager.getTransaction().begin();

    FancyEntity fancyEntity = new FancyEntity(id);
    entityManager.persist(fancyEntity);
    int updateServerHealthCheckTimestamp = entityManager.createQuery("update FancyEntity item set item.value = ?2 where item.id = ?1").setParameter(1, id).setParameter(2, value).executeUpdate();
    assertEquals(1, updateServerHealthCheckTimestamp);

    FancyEntity checkResult = entityManager.find(FancyEntity.class, id);
    assertEquals(1234L, checkResult.getValue()); // <- this assert fails

    entityManager.getTransaction().commit();
}

with

@Entity
public class FancyEntity {
    @Id
    private String id;
    @Column
    private long value;
    public FancyEntity(String id) {
        this.id = id;
        this.value = 0;
    }
    public FancyEntity() {
    }
    public long getValue() {
        retu value;
    }
}

and

<persistence-unit name="test-pu"
                  transaction-type="RESOURCE_LOCAL">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <class>com.fancypackage.FancyEntity</class>

    <properties>
        <property name="eclipselink.logging.level" value="SEVERE"/>
        <property name="javax.persistence.jdbc.driver" value="org.hsqldb.jdbcDriver" />
        <property name="javax.persistence.jdbc.url" value="jdbc:hsqldb:mem;sql.enforce_strict_size=true;hsqldb.tx=mvcc" />
        <property name="eclipselink.ddl-generation" value="drop-and-create-tables" />
        <property name="eclipselink.ddl-generation.output-mode" value="database" />
        <property name="eclipselink.logging.level.sql" value="FINE"/>
        <property name="eclipselink.logging.parameters" value="true"/>
    </properties>
</persistence-unit>

Result is

java.lang.AssertionError: 
Expected :1234
Actual   :0

It seems there is some cache that is not invalidated by the update query. checkResult and fancyEntity are the same object. Forcing the refresh using entityManager.refresh(checkResult). The weirdest thing is that a select is issued for retrieving checkResult (seen in the eclipselink log), still its result is not taken into account. Same behavior using MySQL rather than HSQL.

Any hint on what could be wrong ?