When a issue is assigned to a user, the history tab record the user display name and user_key. As a result, when the user changed the username, JIRA issue history tab will still be showing user_key.
- Create a user(lets say 'test') and using the user, perform certain actions on any issue (like adding issue links, comments etc)
- Notice that the issue history tab shows changes made by this user 'test'.
- Now rename this user from administration console giving it a new username (say 'testabc').
- Now make some more changes to the issue using this renamed user.
- Now go to the history tab and notice that the old username 'test' is still being used. The new username 'testabc' is never used in the history tab.
- Instead of using user_key (which is not editable via UI, issue's history tab should show username instead, as it's more relevant to the users.