The Authorization checks in Camunda are case-sensitive meaning that it treats MelissP and melissp as two different people.

On windows logins via LDAP are case-insensitive meaning that a person can logins with MelissP or melissp and is the same single person.

For full details please see:
https://groups.google.com/forum/#!topic/camunda-bpm-users/Kg5x4PBMDOI