Jira Server Core version: 8.1.0
Symptom:
User uses @ to mention someone in the company in a ticket comment. The user gets the list of users and clicks on the user. It renders to "[~username]" literal text not a hyperlink with the name and blue with link.
Testing done:
1. Checked user has access to Browse permissions(global permissions set to allow users to do mentions), also user role.
2. Tried having the user save the comment even without rendering, after its saved. The render is completed. So it works after but not before.
3. If you type [~ you get a list of users but when you select user it goes back to text, if the user is admin it works fine creating the link in blue before submitting the comment.
4. Cleared cache, rebooted, same browser (chrome).
5. Checked the rendering on the comment field, shows Wiki style rendering.
6. See images how it looks for the user and for admin. 
