Cannot add Approvers on the Customer Portal

Summary

If project setting not allow customers to search another customer by email, when adding Approvers, cannot add one by entering email for the customers
with "QM" generic number as customer username.

Steps to Reproduce

1. Make sure your project doesn't have autocomplete on the approver field in the customer portal (i.e. turn 'Who can customers share requests with?' option in Customer permissions to 'Other customers in their org'.
2. Create a new customer account and make sure the username have the customer account id (qm:xxxx)
3. Then , login to Customer Portal with another customer account.
4. Make sure the form have Approvals field , then add the newly created account as approval. Use the customer email.

Expected Results

Successfully add the customer as approvals.

Actual Results

Display error :-

Could not find usernames: test2@some.com

Notes

This behaviour may also occur in other locations - e.g. mentions in comments, and the participants field.

Workaround

1. Change project settings to allow customers see other's emails (i.e. turn 'Who can customers share requests with?' option in Customer permissions to 'Other customers in their org'.); or
2. The agent need to add the approvals from JIRA; or
3. Use the username (QM id); or
4. Migrate the customer account to Atlassian Account. Then , edit the username to email.