Summary

When I invite a new user to my repository > Settings > User and group access.
The new user receives the invitation email.
When the new user accepts the invitation, it allows the new user to signup on id.atlassian.com.
However, it only allows the new user to signup on id.atlassian.com, there's no redirect or options for the new user to signup for Bitbucket.org.

The tendency is that I will need to ask the new user to signup to Bitbucket.org manually and re-add the new user to the repository group based on the new user's created username.

How to Replicate

1. Invite a new user to a repository
2. Accept the invitation via email
3. Sign up to id.atlassian.com (from the invitation email)
4. Verify the email sent via email (from id.atlassian.com)

Workaround

Ask a new user to signup to id.atlassian.com and bitbucket.org first before inviting to the repository.