ProjectLead not exporting correctly after editing username

When a user that is the project leader edits is username, the exporter of that field using ${fullname:ProjectLead} not works.

Steps to reproduce:
1. Add a new template with the field: ${fullname:ProjectLead}
2. Go to user management
3. Edit a user and update the username of a project lead.
4. Go to an issue of that project, and export with the template previous created.
5. The result is the field: ${fullname:ProjectLead}