No merge-requests/ references are visible in git repo

According to the Gitlab docs, merge requests should appear as named references under refs/merge-requests/*/head.

Using git ls-remote, I am unable to see any refs/merge-requests/* references for either my repositories or even this repo. Even after adding to .git/config as detailed in the above docs page, no refs are fetched.

For gitlab-ce, I see ref/tags/*, ref/remotes/* and ref/heads/*, but no refs/merge-requests/* despite there being 55 open Merge Requests.