Slash command not working when using default merge request template setting

Summary

When I add a default merge request template with a slash command /assign @mark-veenstra in it to ayto-assign the merge request to an user, the slash command is not executed, but displayed in the issue description.

When opening a merge request manually and add a /assign @mark-veenstra in it, it does auto-assign the merge request. Only problem is the default template doesn't.

Steps to reproduce

Add the following merge request default template to Settings --> General --> Merge request settings --> Default description template for merge requests

/assign @mark-veenstra

This is the default template, for testing auto-assign

Now open an new issue and press the Create merge request button in the UI. It will create a new branch and a merge request with the WIP status. Only the merge request is not assigned to the user added in the slash command.

Example Project

https://gitlab.com/mark-veenstra/minimal-ruby-app/merge_requests/2

What is the current bug behavior?

Slash command is not executed from the default merge request template

What is the expected correct behavior?

That the slash command is executed

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com