Hibernate doesn't remove object from collection with children in specific case

Please, see method testCollections(). Two objects are created and inserted to collection. Then one of them is removed from collection. Everything works perfect, single row is added in DB. But if we execute any sql query before removing object from collection, hibernated assigns PK for new objects and they are stored in DB both, regardless that in collection is single object... Any idea how to explain it to hibernate?

    @Entity
    @Table(name = "animalowner")
    public class Owner {
        @Id
        @Column
        private Long id;
        @Column(name = "owner_name")
        private String name;
        @OneToMany(fetch = FetchType.EAGER, targetEntity = Animal.class, cascade = { CascadeType.ALL }, orphanRemoval = true)
        @JoinColumn(name = "owner_fk")
        private Set<Animal> animals;
        ......


@Entity
@Table(name = "animals")
public class Animal {
    public Animal(String name, Owner owner) {
        this.name = name;
        this.owner = owner;
    }
    public Animal() {
    }
    @Id
    @GeneratedValue(generator = "animal_generator")
    @SequenceGenerator(name = "animal_generator", sequenceName = "animal_sequence")
    private Long id;
    @Column(name = "cat_name")
    private String name;
    @ManyToOne(targetEntity = Owner.class, fetch = FetchType.EAGER)
    @JoinColumn(name = "owner_fk")
    private Owner owner;
    .........



@Component
public class SomeService {
.....
 @Override
    @Transactional
    public void testCollections(){
        Owner owner = repository.loadOwnerById(1L);
        Set<Animal> animals = owner.getAnimals();
        Animal animal1 = new Animal("animal1", owner);
        Animal animal2 = new Animal("animal2", owner);
        animals.add(animal1);
        animals.add(animal2);

        //IF any SQL called here, hibernate assigns primary keys for animal1 and animal2,
        //and 2 objects are saved to database. 

        animals.remove(animal1);
    }
.....