Failed sync of user from Jira to confluence after changing the user name

Summary

Users sync between Jira and Confluence is not successful after changing username on Jira side

Environment

• Confluence 5.9.10
• Jira 7.x

Steps to Reproduce

1. Set a Jira instance with Internal Directory, create a user with username: 'BOSMADA'
2. Set confluence and delegate authentication to jira and sync users
3. Set and AD in Jira, crate a user with username: 'bosmada'
4. Deactivate 'BOSMADA' from the Jira internal directory and change the user name to 'BOSMADA_internal'
5. Sync Jira with AD, the new user is there and able to login
6. Sync confluence with Jira

Expected Results

The new user bosmada from the JIRA AD should be in confluence and should be able to login

Actual Results

The new user bosmada from the JIRA AD is not synced and can't login

Workaround

flushing the cache and synchronizing again brings the new user to confluence, he is able to login.