Issue Summary

When we try to mention a customer in the comment section via a transition screen the customer doesn't gets added to the Request Participant field. However, it works when mentioning a customer directly to the comment section.

Steps to Reproduce

1. Create a JSM project and then create a new ticket
2. Mention a customer in the comment section and submit via "Share with customer" button. This will add the mentioned user in the Request participant field and works as expected.
3. Now try to transition the issue and mention the user in the comment section and transition the issue.

Expected Results

The customer/user should be added to the Request participant field. 

Actual Results

User is not added to the Request Participant field only the comment gets added to the ticket.

As per https://confluence.atlassian.com/servicemanagementserver/adding-request-participants-939926441.html there is no such limitation mentioned.
Add participants by mentioning them

You can also add participants by mentioning them in the description or comments. They will be immediately added as a participants and will receive a notification about it (if the Participant added notification is enabled).

• Agents: You can mention anyone in the project from the issue view or the customer portal view. Note that users mentioned within internal comments are not added as request participants.

• Customers: You can mention any user that you're allowed to add as a request participant from the customer portal view.

Workaround

As a workaround Automation for Jira can be used to update the Request Participant field.

Scenario -6 mentioned in the KB article - https://support.atlassian.com/automation/kb/how-to-update-the-request-participants-or-a-multi-user-picker-field-from-the/ 

• Add the Edit Issue action

• Scroll down to Additional fields, and use the JSON formula below:

{
    "update": 
{
        "Request Participants": [

   {{#issue.comment.last.body.split("[-,;]").substringAfterLast("[~").substringBeforeLast("]")}}{"add": 
{"name":"{{.}}"}}{{^last}},{{/}}{{/}}
        ]
    }
} 

Versions Tested

Please confirm all versions that have been tested for this issue, and indicate whether the tested version is affected or not affected, below: