JPA 主键生成策略为 Table 时，初始主键值为什么不是预期的值？

Question

各位大佬帮帮小弟吧。求求了！！！

@Id
@GeneratedValue(strategy = GenerationType.TABLE, generator = "ID_GENERATOR")
@TableGenerator(name = "ID_GENERATOR", table = "jpa_id_generators", pkColumnName = "PK_NAME", pkColumnValue = "CUSTOMER_ID", valueColumnName = "PK_VALUE")
public Integer getId() {
    return id;
}

Customer customer = new Customer();
customer.setAge(19);
customer.setEmail("[e-mail]");
customer.setLastName("tc");
customer.setCreatedTime(new Date());
customer.setBirth(new Date());
entityManager.persist(customer);

按理来说，allocationSize 默认为 50，initialValue 默认为 0，不写的话 id 就是从 50 开始。实际上是从 -47 开始。allocationSize 我赋值为 100，id 就从 -97开始，这是怎么回事？

这是配置文件：

<persistence-unit name="jpa-1" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
<!-- 添加持久化类 -->
<class>jpa.helloworld.Customer</class>
    <properties>
        <property name="hibernate.connection.url" value="jdbc:mysql:///jpa?serverTimezone=UTC"/>
            <property name="hibernate.connection.driver_class" value="com.mysql.cj.jdbc.Driver"/>
            <property name="hibernate.connection.username" value="root"/>
            <property name="hibernate.connection.password" value="1024"/>
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect"/>
            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.format_sql" value="true"/>
            <property name="hibernate.hbm2ddl.auto" value="update"/>
    </properties>
</persistence-unit>