OptimisticLockRetryInterceptor retry causes data update instead of insertion when persisting custom entity using Pluggable Variable Persistence

public byte[] marshal(Context context,
                          ObjectOutputStream os, 
                          Object object) throws IOException {
        Object id = getClassIdValue(object);
        String entityType = object.getClass().getCanonicalName();
        
        EntityPersister entityPersister = persister.get();

        if (!entityPersister.isPersited(object)) {
            EntityManager em = getEntityManager();
            if (id == null) {
                em.persist(object);
                id = getClassIdValue(object);
            }
            addMapping(id, entityType, object, os, em);
            em.merge(object);
            
            entityPersister.processed(object);
            
            // since this is invoked by marshaller it's safe to call flush
            // and it's important to be flushed so subsequent unmarshall operations
            // will get update content especially when merged
            em.flush();
        }
        ByteArrayOutputStream buff = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream( buff );
        oos.writeUTF(entityType);
        oos.writeObject(id);
        oos.close();
        return buff.toByteArray();
    }