Removing user from LDAP doesn't clear LDAP group membership

Reproduction steps:
1. Setup generic LDAP user repository (RW), with jira-users, jira-developers, jira-administrators groups.
2. Create user for John Smith as js@x.com.
3. Add him to jira-administrators group.
4. Remove user js@x.com (John changed the company).
5. Create user for Jake Sunny as js@x.com.

Result: newly hired Jake Sunny is administrator, now.