If you want to use object duplication possibilities, you have to use the CoreBundle custom CRUD controller in your admin service:

      librinfo_varieties.admin.variety:
        class: Librinfo\VarietiesBundle\Admin\VarietyAdminConcrete
        arguments: [~, Librinfo\VarietiesBundle\Entity\Variety, BlastCoreBundle:CRUD]
        tags:
            - name: sonata.admin
              manager_type: orm
              group: admin
