Incorrect diff when suggesting change to markdown list

Summary

Suggesting change to markdown list results in incorrect diff rendering

Steps to reproduce

  1. Create a merge request to a markdown file with a checklist
  2. Suggest a change to one of the items

Example Project

gitlab-com/www-gitlab-com!17590 (diffs, comment 126608856)

What is the current bug behavior?

The suggested change diff doesn't show the leading -

What is the expected correct behavior?

The suggested change diff should show the leading -

Relevant logs and/or screenshots

Input Current (bug) Expected
Screen_Shot_2018-12-21_at_11.10.57_AM Screen_Shot_2018-12-21_at_11.09.41_AM Screen_Shot_2018-12-21_at_11.10.10_AM

Output of checks

This bug happens on GitLab.com