Git ghost references

I seem to have a "ghost reference" - ie. I can check out a reference that doesn't appear to exist. Does anyone know what might cause this?

~/gaf-cvs (project-membership)$ g show-ref | grep production
~/gaf-cvs (project-membership)$ g gc --prune=now
Counting objects: 117306, done.
Delta compression using up to 2 threads.
Compressing objects: 100% (25270/25270), done.
Writing objects: 100% (117306/117306), done.
Total 117306 (delta 83839), reused 117283 (delta 83820)
~/gaf-cvs (project-membership)$ g co production
Note: checking out 'production'.

You are in 'detached HEAD' state. You can look around, make experimental changes and commit them, and you can discard any commits you make in this state without impacting any branches by performing another checkout.

If you want to create a new branch to retain commits you create, you may do so (now or later) by using -b with the checkout command again. Example:

  git checkout -b new_branch_name

HEAD is now at ae5b621... Merge branch 'master' of git.freelancer.com:production ~/gaf-cvs ((no branch))$