checklist boxes cannot be checked in incidents

Summary

Checklists like - [ ] foo, in issues, make a HTML checklist that can be "checked" with the mouse when the issue is saved. On incidents, that feature does not work correctly, failing with the error "Someone edited this incident at the same time you did."

Steps to reproduce

1. go on a project on gitlab.com, in Monitor -> Incidents
2. click "Create incident"
3. choose a title, make a checklist in the body, for example with the text - [ ] test
4. save the incident
5. try to check the checkbox

Example Project

• failing issue, incident: anarcat/test#2 (closed)
• working issue, normal issue: anarcat/test#1 (closed)

What is the current bug behavior?

The checkbox, when checked, pops a red warning at the top of the page saying:

Someone edited this incident at the same time you did. The description has been updated and you will need to make your changes again.

The box is checked, but not really: when reloaded the page doesn't show the box saved, or when edited, the "box" is empty ([ ]).

What is the expected correct behavior?

The box should be checked even after reload or, when edited, the "box" should be "checked" ([x]).

Relevant logs and/or screenshots

Failing issue:

After reload:

Working issue, before:

after checking and reload:

Output of checks

This bug happens on GitLab.com

Possible fixes

There are many issues related to checkboxes like this:

• #352695 (closed) (nbsp)
• #64697 (inside block quotes)
• #355983 (closed) (numbered list)
• #357686 (closed) (unicode spacing)

Most of those have been fixed, and are not related to this issue, at least the issue is reproducible without the above special circumstances. My current theory is that it's specific to incidents, but before filing this issue I wasn't actually sure what the underlying cause was.