Hi, please consider the following example.

docker pull artifactory.mycompany.com/docker-dev/appname/dev:latest
docker tag artifactory.mycompany.com/docker-dev/appname/dev:latest artifactory.mycompany.com/docker-dev/appname/test:latest
docker push artifactory.mycompany.com/docker-dev/appname/test:latest

Now if I try to do the same with the plugin then it doesn't work.

image = docker.image("artifactory.mycompany.com/docker-dev/appname/dev:latest")
image.pull()
image.tag("artifactory.mycompany.com/docker-dev/appname/test:latest")
image.push()

I get error :

Error parsing reference: "artifactory.mycompany.com/docker-dev/appname/dev:artifactory.mycompany.com/docker-dev/appname/test:latest" is not a valid repository/tag: invalid reference format

If I do following

image = docker.image("artifactory.mycompany.com/docker-dev/appname/dev:latest")
image.pull()
image.push("artifactory.mycompany.com/docker-dev/appname/test:latest")

I get error: 

Error parsing reference: "artifactory.mycompany.com/docker-dev/appname/dev:artifactory.mycompany.com/docker-dev/appname/test:latest" is not a valid repository/tag: invalid reference format

If I do following

image = docker.image("artifactory.mycompany.com/docker-dev/appname/dev:latest")
image.pull()
image.push("artifactory.mycompany.com/docker-dev/appname/test:latest artifactory.mycompany.com/docker-dev/appname/test:latest")

I get following error

"docker tag" requires exactly 2 arguments.
See 'docker tag --help'.

Usage: docker tag SOURCE_IMAGE[:TAG] TARGET_IMAGE[:TAG]

Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE

In the logs I see following

artifactory.mycompany.com/docker-dev/appname/dev:latest artifactory.mycompany.com/docker-dev/appname/dev:latest:artifactory.mycompany.com/docker-dev/appname/dev:latest artifactory.mycompany.com/docker-dev/appname/test:latest