test.sh

docker build
>> built XXXXX

docker tag registry/test/FOOBAR:my-tag

docker push registry/test/FOOBAR
>> pushes XXXXX to registry/test/FOOBAR (uploaded)

docker build
>> built XXXX1

docker tag registry/test/FOOBAR:my-new-tag
docker push registry/test/FOOBAR
>> pushes XXXXX to registry/test/FOOBAR:my-tag (skipped as pushed before)
>> pushes XXXX1 to registry/test/FOOBAR:my-new-tag (uploaded)

-- another machine --

docker pull -t my-new-tag registry/test/FOOBAR
>> pulls registry/test/FOOBAR:my-tag (XXXXX)

docker pull -t my-new-tag registry/test/FOOBAR
>> pulls registry/test/FOOBAR:my-new-tag (XXXX1)

##### This is great. #####
##### However. If (for cleanup purposes) the layers and image attached to registry/test/FOOBAR:my-tag are deleted from the registry, this will happen... #####

docker push registry/test/FOOBAR
>> pushes XXXXX to registry/test/FOOBAR:my-tag (uploaded)
>> pushes XXXX1 to registry/test/FOOBAR:my-new-tag (uploaded)

##### Now we're back where we started, it pushed my-tag which was actually deleted from the registry on purpose #####