docker registries from same project do not share images nor layers

gitlab docker registry supports now different images names:

GitLab supports up to 3 levels of image names. The following examples of images are valid for your project:

The problem is that foreach image name, it seems to create an independent registry. If you upload the very same docker image to

myproject:tag
myproject/optional-image-name:tag

it will still upload it. I can't see the rationale for this (but I can see the rationale for not sharing layers across projects).