Removed user can still be mentioned on an issue user commented on

Issue Summary

Removed user can still be mentioned on an issue user commented on

Steps to Reproduce

• create a user
• get the user to comment / add attachment
• remove the user from site
  → You can still mention the user on the issue
  → You would not be able to mention the user on other issues that he has not commented on

Expected Results

Removed user should not be in the @mention list

Actual Results

Removed user is in the @mention list for that particular issue

User is removed from site so notification will not be sent. Hovering over the user will indicate that the user is an invalid user.

Workaround

Currently there is no known workaround for this behaviour. A workaround will be added here when available