MR approvals don't get cleared when using the rebase button

Steps taken

0. Confirm that 'Remove all approvals in a merge request when new commits are pushed to its source branch' is enabled in repo settings
1. Have someone else create MR from test_branch to master
2. Push a new commit to master
3. Press Approve button on MR page
4. Press Rebase button on MR page
5. Wait an eternity for the rebase to complete 😈
6. Refresh the MR page

A new pipeline started which confirms that the HEAD changed, but the approval remained.

This seemed to be a bug to me, as rebasing adds new commits to the source branch and my expectation based on that setting's description is that this should remove approvals. Apparently, it's desired behavior though, so this makes my issue more of a feature request.

System versions

GitLab 10.2.1-ee
GitLab Shell 5.9.4
GitLab Workhorse v3.3.1
GitLab API v4
Gitaly 0.52.0
GitLab Pages 0.6.0
Git 2.13.6
Ruby 2.3.5p376
Rails 4.2.8
postgresql 9.6.1