We have different user-roles. We add a comment. We mention somebody from user-role = 1 in this comment. After this we restrict this comment to user-role = 2 and save it.

The user which we have mentioned (user-role = 1) gets an email with the text we have added in the comment. So in the mail he can see the text!
If he opens the issue he cannot see the comment because it is only viewable for
user-role = 2.

In our suggestion the user should not see the content of this comment in the mail JIRA sends to him. Because the comment was restricted to an user group where this user does not belong to.