openstack image-delete can not delete image -

our openstack kilo , manage vmware 6.

we backup using following command:

nova backup 762ecf86-f5eb-4c7c-a512-3cf15e23dd1a \   backup-snapshot-a-daily-$(date "+%y%m%d-%h:%m")   daily 1   

a new image appears when running glance image-list.

to delete it, run glance image-delete without errors.

we run glance image-list again , find image has disappeared.

yet in vsphere client, in vmfs, directory still here.

after 1 minute, run glance image-list again, image still there.

so how can delete image?