This issue was discovered in the docker-workflow-plugin, which has a dependency on docker-commons-plugin.
Given the following pipeline code:

docker.withRegistry('http://localhost:5000/') {
   def dockerImage = docker.image('localhost:5000/test-image')
      dockerImage.inside {
         echo "container running on ${port}"
      }
}

The rendered "docker pull" command incorrectly formats the qualified image name as:
localhost:5000/localhost:5000/test-image

I have submitted a PR that adds a condition to check whether or not the image name already contains the registry prefix to avoid appending again.

https://github.com/jenkinsci/docker-commons-plugin/pull/56