Deleted LDAP user's assigned issues cannot be searched in Issue Navigator even though it shows in Project Overview

======== Steps to reproduce =======

1. Connect JIRA to LDAP directory and sync. (Connector type)
2. Assign some issues in a project to an LDAP user in JIRA.
3. Delete the user in LDAP, and sync again in JIRA.
4. Going to the Project Overview page, the issues tab, we can see that those assigned issues in #2 has become unassigned due to the deleted LDAP user: UnassignedIssue.jpg
5. If you click on the Unassigned link, it will bring you to the Issue Navigator to see the list of unassigned issues. But the list is empty: Filter.jpg

======== Expected Behavior =========

1. The issue navigator should show the unassigned issues. (previously assigned to the deleted LDAP user)

Reindexing does not help.