New merge request description disappears if you change the target branch

Summary

Can't find this on the issue tracker.

This happens when creating a new merge request and have filled out a description, then you want to change the target branch.

Once you have set the target branch you are redirected back to the new merge request page but will have lost everything you typed in the description text box.

Steps to reproduce

Tested on v11.7.0-ee

1. Create new merge request
2. Fill out description (anything)
3. Change target branch
4. Set the target branch
5. Get redirected back to new merge request page
6. See that your description has disappeared

Example Project

N/A

What is the current bug behavior?

You lose everything you typed in the merge request description box

What is the expected correct behavior?

The original description for the merge request, even after we change target branches

Relevant logs and/or screenshots

N/A

Output of checks

This is on our company servers

Results of GitLab environment info

I do not have permissions to run this

Results of GitLab application Check

I do not have permissions to run this

Possible fixes

N/A