Mixed case usernames can break connection between Confluence and JIRA for User Management

Problem

When synchronising a Confluence User Directory that is connected to JIRA, groups do not transfer across due to discrepancies between the user_name (mixed case).

To Recreate

1. JIRA: Add a new user to JIRA Internal Directory. This user will be enforced lowercase, e.g.: joe.bloggs@example.com.
2. JIRA: Create several groups and add that user to those groups, e.g.: Sample Group.
3. Confluence: Connect Confluence to JIRA for User Management. The synchronisation will create a User Directory in Confluence with a lower case user.
4. JIRA: Add a LDAP connection to JIRA to fetch the same user, however in mixed case, e.g.: Joe.Bloggs@example.com from an external LDAP/AD.
5. Confluence: Synchronise the JIRA Server User Directory. At this point it should fail with an error like the below:
   atlassian-confluence.log

   2012-06-05 12:06:50,354 ERROR [scheduler_Worker-7] [crowd.embedded.hibernate2.HibernateMembershipDao] addAllUsersToGroup joe.bloggs@example.com into Sample Group
   2012-06-05 12:06:50,355 ERROR [scheduler_Worker-7] [crowd.embedded.hibernate2.HibernateMembershipDao] addAllUsersToGroup Please try to resolve any errors with these users and groups, and try again.
   2012-06-05 12:06:50,355 WARN [scheduler_Worker-7] [atlassian.crowd.directory.DbCachingRemoteChangeOperations] addUserMembershipsForGroup Could not add the following missing users to group [Sample Group ]: [joe.bloggs@example.com]
   

I believe this is to do with differences between the cwd_user.user_name, maybe it's not using cwd_user.lower_user_name?

Workaround

Remove the Confluence 'JIRA Server' User Directory and add it again. When it is added again, it will create the users with the same case as the LDAP/AD directory in JIRA.