Customers with Mixed-case Username can't Share/Unshare a Request without Modify Reporter permission

Issue Summary

If Modify Reporter permission is revoked from Service Desk Customer - Portal Access, then customers with mixed-case username can't edit request participants from Customer Portal.

Steps to Reproduce

1. Edit an SD project's permission scheme and revoke Modify Reporter permission from Service Desk Customer - Portal Access
2. Create a customer account with mixed-case username e.g. Adam
3. Raise a request on behalf of Adam in the above project and add a participant to it
4. Log in as Adam via Customer Portal
5. Try to add a new participant to or remove the existing one from the above request

Expected Results

Participants can be added or removed normally.

Actual Results

• 500 error is thrown for adding participants (sharing)
• 400 error is thrown for removing participants (unsharing)

Workaround

Grant Modify Reporter permission to Service Desk Customer - Portal Access. This doesn't allow customers to modify reporters, so shouldn't be a problem at all.