Manual jobs block merging a MR

Summary

Any manual job is not run prevents merging a PR even if project settings don't require pipelines to succeed

Steps to reproduce

Configure .gitlab-ci.yml to have a job with when: manual. Start a merge request and let the pipeline run automatically, without touching manual steps.

Example Project

What is the current bug behavior?

Merge request has 'Merge' button disabled with message:

Pipeline blocked. The pipeline for this merge request requires a manual action to proceed

What is the expected correct behavior?

My project has Settings » General » Merge checks » Pipelines must succeed disabled. This means a pipeline that fails does not block merging a MR. Now I have a pipeline that finished all started jobs with success but there is no way for me to merge it from UI. This does not make sense.

There were numerous discussions about this topic in the old bug tracker, but I don't see any of the issues moved here: gitlab-foss#41114 (moved) gitlab-foss#60334 (moved)

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info

GitLab Community Edition 12.7.5

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)