undefinied is displayed when mentioning user in Jira

Summary

When mentioning user via wysiwyg editor using @ undefined is displayed next to username

Steps to reproduce

1. Start commenting / Edit existing comment (or perform action in the description field)
2. use @ and start typing the username

Actual Result

after user first name there is the undefined text displayed (see the wysiyg-editor-undefined.png)

Expected Result

User first name and last name is followed by username without the underfined text (I can see that email is being used on other instances).