Notifications sending user Account ID instead of full name

Issue Summary

When using having the user preference for Email notifications format set to Text the email notifications from JIRA will contain the user's Account ID instead of their full name.
https://atl-vertigo-kasper.atlassian.net/secure/ViewPersonalSettings.jspa

Steps to Reproduce

1. Set your notifications format to Text at:

   https://{instance}.atlassian.net/secure/ViewPersonalSettings.jspa
   

2. Have another user mentioning you on a ticket or comment.

Expected Results

The notification sent to your email should contain the user's full name.

Actual Results

The notification received only have the user Account ID:

Workaround

Set your Email notifications format set to HTML.
You can also change the default user preferences to HTML at:

https://{instance}.atlassian.net/secure/admin/ViewUserDefaultSettings.jspa

This will apply the change to all users to from your instance.