missing signature key calling hub.Manifest()

[pcittadini]

Trying to get V1 manifest produces:
"missing signature key" error, while trying to get V2 manifest works fine.

Trying the API call directly with curl works also:
curl --netrc-file ~/.registry_auth -XGET https://docker.myregistry.com/v2/ops/myimage/manifests/latest

This is the code that produces the error:

hub, err := registry.New(conf.DOCKER_REGISTRY, conf.DOCKER_REGISTRY_USR, conf.DOCKER_REGISTRY_PWD)
if err != nil {
	return nil, err
}

manifest, err := hub.Manifest(image, tag)
if err != nil {
	log.Print(err.Error())
	return nil, err
}

The interesting part of the manifest for me is the History array section, which contains labels (absent when calling the ManifestV2 method).

Thanks