Custom field Value is Not Included in Mentioned Notification

Summary

When we included some custom fields on email templates it works fine except for mention template where the custom fields just don't get a value and is always empty.

Environment

• JIRA version 7.1.2
• JIRA version 7.2.6

Steps to Reproduce

1. Go to atlassian-jira/WEB-INF/classes/templates/email/text
2. Add a custom field value to be included in issue commented and issue mentioned notification as mentioned in Adding Custom Fields to Email
3. Now comment and issue as well as mentioned an user in a ticket.

Expected Results

In both notification send by JIRA the custom field value is included

Actual Results

Only for issue commented the custom field value is included while for issue mentioned notification the custom field value is not included.

Notes

The customization works for all templates except for issue mentioned templates

Workaround

Currently there is no workaround