Comments made in a commit on an MR disappear from Changes tab

Summary

Trying to add a comment in a project when clicking a specific commit of a MR makes the comment dissapear from the MR changes tab. The comment is shown in the discussion tab though.

Steps to reproduce

• Have a MR with more than one commit
• Click commits tab
• Click commit
• Make a comment

Example Project

https://gitlab.gnome.org/World/ShellExtensions/desktop-icons/merge_requests/27/diffs?commit_id=13550b540f4de96ba5dbbd3524e20840582ec564

There, trying to make a comment in the FileItem.js file makes the comment dissapear. I can give you access if you need to test, we don't mind for you testing directly there.

What is the current bug behavior?

Comment disappear from the changes tab.

What is the expected correct behavior?

Comment stays

Relevant logs and/or screenshots

This is with GitLab CE 11.4.

I cannot see any relevant logs in the admin panel. Here's a screen recording of the issue though:

Screencast_from_10-25-2018_02_24_22_PM

Output of checks

(If you are reporting a bug on GitLab.com, write: This bug happens on GitLab.com)

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:env:info)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production)

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)