API using url encoded paths is broken

According to documents here https://docs.gitlab.com/ce/api/README.html#namespaced-path-encoding a project with the path some_namespace/some_name should be accessible via the API using a url like

https://host.domain/api/v4/projects/some_namespace%2Fsome_name

This never works. The accuracy of the path can be confirmed by using the search API

https://host.domain/api/v4/projects?search=some_name

and checking the element "path_with_namespace" in the returned record, but the documented API form using encoded paths simply does not work.

This is from {"version":"9.2.1","revision":"df00a75e"}