Setting gitlab_shell['ssh_path_prefix'] in /etc/gitlab/gitlab.rb has no effect

Summary

Customizing the SSH path prefix in /etc/gitlab/gitlab.rb has no effect.

Steps to reproduce

When I add

gitlab_shell['ssh_path_prefix'] = 'test'

to /etc/gitlab/gitlab.rb and run gitlab-ctl show-config, the output contains

[...]
{
  "gitlab": {
    "gitlab-shell": {
      "ssh_path_prefix": "test",
      [...]
    }
    [...]
  }
  [...]
}
[...]

However, even after reconfiguring, in gitlab-rails console I get

> Gitlab.config.gitlab_shell['ssh_path_prefix']
=> "git@gitlab.example.com:"

Most importantly, the path prefix in the web interface does not change.

Example Project

This behavior is seen both in a server install and on the docker image of GitLab CE.

What is the current bug behavior?

The default value for ssh_path_prefix is used.

What is the expected correct behavior?

The value as set in /etc/gitlab/gitlab.rb is used.

Results of GitLab environment info

Only the docker install is under my full control:

System information
System:		
Current User:	git
Using RVM:	no
Ruby Version:	2.6.3p62
Gem Version:	2.7.9
Bundler Version:1.17.3
Rake Version:	12.3.3
Redis Version:	3.2.12
Git Version:	2.22.0
Sidekiq Version:5.2.7
Go Version:	unknown

GitLab information
Version:	12.5.2
Revision:	49482945d28
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	PostgreSQL
DB Version:	10.9
URL:		http://gitlab.example.com
HTTP Clone URL:	http://gitlab.example.com/some-group/some-project.git
SSH Clone URL:	git@gitlab.example.com:some-group/some-project.git
Using LDAP:	no
Using Omniauth:	yes
Omniauth Providers: 

GitLab Shell
Version:	10.2.0
Repository storage paths:
- default: 	/var/opt/gitlab/git-data/repositories
GitLab Shell path:		/opt/gitlab/embedded/service/gitlab-shell
Git:		/opt/gitlab/embedded/bin/git

Results of GitLab application Check

gitlab-rake gitlab:check SANITIZE=true

Checking GitLab subtasks ...

Checking GitLab Shell ...

GitLab Shell: ... GitLab Shell version >= 10.2.0 ? ... OK (10.2.0)
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Internal API available: OK
Redis available via internal API: OK
gitlab-shell self-check successful

Checking GitLab Shell ... Finished

Checking Gitaly ...

Gitaly: ... default ... OK

Checking Gitaly ... Finished

Checking Sidekiq ...

Sidekiq: ... Running? ... yes
Number of Sidekiq processes ... 1

Checking Sidekiq ... Finished

Checking Incoming Email ...

Incoming Email: ... Reply by email is disabled in config/gitlab.yml

Checking Incoming Email ... Finished

Checking LDAP ...

LDAP: ... LDAP is disabled in config/gitlab.yml

Checking LDAP ... Finished

Checking GitLab App ...

Git configured correctly? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config up to date? ... yes
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory exists? ... yes
Uploads directory has correct permissions? ... yes
Uploads directory tmp has correct permissions? ... skipped (no tmp uploads folder yet)
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
Projects have namespace: ... 
1/1 ... yes
2/2 ... yes
2/3 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.5.3 ? ... yes (2.6.3)
Git version >= 2.22.0 ? ... yes (2.22.0)
Git user has default SSH configuration? ... yes
Active users: ... 3
Is authorized keys file accessible? ... yes

Checking GitLab App ... Finished


Checking GitLab subtasks ... Finished

Possible fixes

I could not find anything out of the ordinary in config/initializers/1_settings.rb.