Unable to create an identical merge request after reverting the first merge request

A colleague accidentally merged a request which hadn't been reviewed, I reverted the merge using the request UI so that the merge could be reopened. When trying to create a new merge request just like the first, GitLab says the branches are identical.

Steps to reproduce:

  1. create a new repository and clone it
  2. touch file && git add file && git commit -m "add file" && git push -u origin master
  3. echo change > file && git commit -m "change file" && git push -u origin HEAD:change_file
  4. open a merge request from change_file to master
  5. accept it
  6. revert it without creating a new merge request for the revert, git pull && cat file will show the revert worked
  7. try to open a merge request from change_file to master, it says there isn't anything to merge.

I also tried closing the merge request then creating a new merge request from a different branch.

Installation details: GitLab 8.7.2 GitLab Shell 2.7.2 GitLab API v3 Git 2.7.4 Ruby 2.1.8p440 Rails 4.2.6 PostgreSQL 9.2.15