Hibernate tries to insert one to one relation without any cascading

The problem

Im having two entities. One is called EntityPojo and the other one is called ChunkPojo. The entityPojo does not know about the ChunkPojo. The ChunkPojo has a 1:1 reference to the EntityPojo. First i save the EntityPojo, then i save the ChunkPojo.

At the time i save the ChunkPojo, hibernate tries to insert the referenced 1:1 EntityPojo which results in an duplicate key exception. But... cascading is disabled, this should NOT happen.

The code

/** The base for all database objects
*/
@MappedSuperclass
public abstract class DatabaseObject extends Component{

    @Id
    public Long id;

    @MapsId
    @JoinColumn(name = "id")
    @OneToOne(cascade = {})
    public EntityPojo entityPojo;
}

@Entity
@Table(name = "entity")
@Access(AccessType.FIELD)
public class EntityPojo {

    @Id public long id;
    public long version;

    public String tag;
    public String typeID;

    public EntityPojo() { }
}

/**
 * A chunk which extends DatabaseObject.
 */
@Entity
@Table(name = "chunk", uniqueConstraints = {@UniqueConstraint(columnNames={"x", "y"})}, indexes = {@Index(columnList = "x,y")})
@Access(value = AccessType.FIELD)
@SelectBeforeUpdate(value = false)
public class ChunkPojo extends DatabaseObject {

    public int x;
    public int y;
    public Date createdOn;
}

public static void main(String[] args){

        var enitity = new EntityPojo();
        enitity.id = 1;
        enitity.tag = "player";
        enitity.typeID = "1:1";

        var chunk = new ChunkPojo();
        chunk.x = 10;
        chunk.y = 11;
        chunk.entityPojo = enitity;
        chunk.id = enitity.id;

        syncDatabase.save(enitity);  // Just calls session.persist - works fine 
        syncDatabase.save(chunk);    // Also calls session.persist - exception
}

Question

Why does hibernate try to insert the referenced 1:1 relation when i clearly did not used any cascading here ? And how can i prevent it from happening ?

Glad for any help on this topic ! It drives me crazy ! Thanks !

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