Summary

Custom Field User Picker (multiple users) is removing the users that had their usernames changed when you're editing the field.

You can check here a short video about this problem.

Steps to Reproduce

1. Create a User: charlie
2. Change their user_name to atlassian (customer could have it done themselves prior to the username deprecation). This will cause the user_name to be different from the user_key.
3. Create a User Picker (multiple users) custom field and associate it to a project.
4. Create an issue, and under the user picker custom field, include atlassian user and save the field using the Old Issue View.
5. Click to edit the field and atlassian user will not be displayed and then click on Save icon and the user will be removed from the field.
6. Add the atlassian user again.
7. Go to the Edit Issue page, the user picker field will not display atlassian user even after you added again.

Expected Results

The users should not be removed from the field while you're editing it.

Actual Results

If you edit a User Picker (multiple users) using the Old Issue View, the users, that had their usernames changed, will be removed from the field. Also, they will not be displayed as a value in the field on the Edit Issue screen.

Workaround

This problem is not happening in the New Issue View, so, in case it's available, you can use it as a workaround.