Creating a user named "Unassigned" causes issue assignees to be mixed up

Issue Summary

If a Jira instance has a user called 'Unassigned' then the assignee related searches get mixed up.

Steps to Reproduce

1. Create a new user on the Jira instance
2. Use the username 'Unassigned' and Full name and email as anything.

Expected Results

Nothing should break and all searches should work normally.

Actual Results

The searches for this Unassigned user and the unassigned issues get mixed up.
Searching like assignee is EMPTY or assignee = Unassigned both show issues that are either unassigned or that are assigned to the 'Unassigned' user.

Notes

Related KBs

• Unassigned issues doesn't follow the swimlane configuration

Workaround

Delete the user 'Unassigned' from the instance.