gitlab CI builds will start and hang if they are disabled and an external (Jenkins) CI Build finishes

Summary

Our Project has a valid .gitlab-ci.yml File and a gitlab runner for ssh configured. Also we have a Jenkins Job, that gets triggered on each push and reports back the result via the GitLab Plugin. Currently we want to use this and disable the internal gitlab CI builds, we did so in the project settings.

Steps to reproduce

The used software is the following (but the bug has been there for months with all versions): Gitlab 8.13 Jenkins (2.27) Gitlab Plugin (1.4.2)

  1. setup the software above, configure a gitlab runner (we used ssh)
  2. configure a .gitlab-ci.yml file for a project. Possibly run a build with it
  3. configure a Jenkins project, we used a Pipeline Project and wrapped the build with gitlabCommitStatus('build') {}
  4. in gitlab setup a push trigger for the Jenkins Job
  5. disable the builds in Gitlab`s project settings
  6. push code to the repository

Expected behavior

Upon a push, the Jenkins Job should start, and pushing the result to gitlab. gitlab should display the result for the commit

Actual behavior

Upon a push, the Jenkins Job starts, and pushes the result to gitlab. gitlab then tries to start a internal CI build and the build will just hang (atelast for a long time)

Relevant logs and/or screenshots

glab

Output of checks

Results of GitLab application Check

Checking GitLab Shell ...

GitLab Shell version >= 3.6.6 ? ... OK (3.6.6)
Repo base directory exists?
default... yes
Repo storage directories are symlinks?
default... no
Repo paths owned by git:git?
default... yes
Repo paths access is drwxrws---?
default... yes
hooks directories in repos are links: ... 
6/1 ... ok
6/3 ... ok
1/5 ... ok
2/6 ... ok
9/7 ... ok
1/8 ... ok
6/9 ... ok
6/10 ... ok
5/11 ... ok
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Check GitLab API access: OK
Access to /var/opt/gitlab/.ssh/authorized_keys: OK
Send ping to redis server: OK
gitlab-shell self-check successful

Checking GitLab Shell ... Finished

Checking Sidekiq ...

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

Checking Sidekiq ... Finished

Checking Reply by email ...

Reply by email is disabled in config/gitlab.yml

Checking Reply by email ... Finished

Checking LDAP ...

LDAP is disabled in config/gitlab.yml

Checking LDAP ... Finished

Checking GitLab ...

Git configured with autocrlf=input? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config outdated? ... no
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory setup correctly? ... yes
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: ... 
6/1 ... yes
6/3 ... yes
1/5 ... yes
2/6 ... yes
9/7 ... yes
1/8 ... yes
6/9 ... yes
6/10 ... yes
5/11 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.1.0 ? ... yes (2.3.1)
Your git bin path is "/opt/gitlab/embedded/bin/git"
Git version >= 2.7.3 ? ... yes (2.7.4)
Active users: 9

Checking GitLab ... Finished

Results of GitLab environment info

System information
System:		
Current User:	git
Using RVM:	no
Ruby Version:	2.3.1p112
Gem Version:	2.6.6
Bundler Version:1.13.5
Rake Version:	10.5.0
Sidekiq Version:4.2.1

GitLab information
Version:	8.13.0
Revision:	053a0a2
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	postgresql
URL:		http://10.99.11.2
HTTP Clone URL:	http://10.99.11.2/some-group/some-project.git
SSH Clone URL:	git@10.99.11.2:some-group/some-project.git
Using LDAP:	no
Using Omniauth:	no

GitLab Shell
Version:	3.6.6
Repository storage paths:
- default: 	/var/opt/gitlab/git-data/repositories
Hooks:		/opt/gitlab/embedded/service/gitlab-shell/hooks/
Git:		/opt/gitlab/embedded/bin/git