Unable to edit a component to set a user with uppercase characters in their username as Component Lead

Summary

When trying to edit an existing component to set a user with uppercase characters in their username as Component Lead for a JIRA Component, an error "The user <username> does not exist."

Users without uppercase characters in their username can be entered without problems.
Selecting a user with uppercase characters in their username is possible when creating a new component.

Environment

• JIRA Cloud (JIRA v1000.5.0)
  Works in JIRA Cloud v7.2.0-OD-03-005

Steps to Reproduce

1. Click on the 'Project settings' menu for a JIRA project
2. Click on the 'Components' link and then click on the ... button and select edit for an existing component.
3. Select a user (with uppercase characters in their username) from the drop down list, and then click Save.

Expected Results

The user selected from the list is saved as the component lead

Actual Results

An error is displayed on screen (nothing appears in the logs):

Workaround

It is possible to edit the existing component using the REST API.