There is an issue with user invitations sent out by JIRA Admins. When the invitation is sent out and the admin renamed the username; user will no longer be able to access the invitation (as the invitation link is referring to the old username). Even if JIRA Admin rename after the user accepted the invitation; they still have to notify users of the change; otherwise user will not be able to log in.

1) Invite user and immediately rename the generated username (I don't want to have a user with this name). In that case the mailed link will fail, because the user in the maillink doesn't exist anymore under that name. Also, I cannot stop the system from mailing to my new user.

2) Invite user, wait for registration and rename afterwards. This confuses my user, because he registered under username A, but this is changed into B right after registration. I cannot explain this to my users.

I believe this issue can be quite confusing and can be a very frustrating experience to the user. Perhaps instead of using the username as a reference; the security token can be used instead? Then any changes to the username will not affect the invitation link.