if all CI stages are manual, only the first one is playable

Summary

If all CI stages are manual, only the first one is playable

Steps to reproduce

image: busybox:latest

stages:
  - stage1
  - stage2
  - stage3
   
build1:
 stage: stage1
 script:
   - echo "stage1"
 when: manual
   
build2:
 stage: stage2
 script:
   - echo "stage2"
 when: manual
 
build3:
 stage: stage3
 script:
   - echo "stage3"
 when: manual

What is the current bug behavior?

Only the first stage is playable. Even, when first stage has been played, we can play other stages.

What is the expected correct behavior?

All stages should be playable

Relevant logs and/or screenshots

Screenshot after stage1 manually played :

Output of checks

None

Results of GitLab environment info

System information
System:         Ubuntu 14.04
Current User:   git
Using RVM:      no
Ruby Version:   2.3.3p222
Gem Version:    2.6.6
Bundler Version:1.13.7
Rake Version:   10.5.0
Redis Version:  3.2.5
Git Version:    2.10.2
Sidekiq Version:4.2.7

GitLab information
Version:        9.0.1
Revision:       0fa55cc
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     postgresql
URL:            https://xxx.xxxxx.fr
HTTP Clone URL: https://xxx.xxxxx.fr/some-group/some-project.git
SSH Clone URL:  git@xxx.xxxxx.fr:some-group/some-project.git
Using LDAP:     yes
Using Omniauth: no

GitLab Shell
Version:        5.0.0
Repository storage paths:
- default:      /var/opt/gitlab/git-data/repositories
Hooks:          /opt/gitlab/embedded/service/gitlab-shell/hooks/
Git:            /opt/gitlab/embedded/bin/git

Results of GitLab application Check

All green

Possible fixes

No idea