gitlab_ci['backup_keep_time'] is ignored

I have set the following in my omnibus GitLab configuration file:

gitlab_rails['backup_keep_time'] = 1814400   # 21 days in seconds
gitlab_ci['backup_keep_time'] = 1814400   # 21 days in seconds

While the gitLab backups are properly pruned, GitLab CI backups continue to exist forever.

Why is there a separate backup option for CI anyway? Now that CI has been integrated into the main product. It would be a lot easier if there was a common configuration and backup as well.