Default description MR template overwrites on edit

Summary

With a default MR description template saved in .gitlab/merge_request_templates/default.md it will show when creating an MR.

However this looks to now also happen when editing an MR, blocking the user from making any changes:

Screen_Recording_2022-01-14_at_15.29.54

This should only happen on new MRs, not existing.

Possible related MR: !76326 (merged)

Steps to reproduce

Have a Default MR Description template file saved in .gitlab/merge_request_templates/default.md and attempt to edit an existing MR. Notice that the description will be overwritten with the template.

Example Project

https://gitlab.com/gitlab-org/quality/gitlab-environment-toolkit

What is the current bug behavior?

Existing MR description gets overwritten by the template.

What is the expected correct behavior?

Existing MR description doesn't get overwritten by the template.

Output of checks

This bug happens on GitLab.com