If you have an instance configured for LDAP login-only its not clear how users or administrators should recover from the scenario where a user forgets to register for a long enough time to void the registration link. In particular, users get thrown into an email registration workflow where they will hit a 400 error.
Original report below:
I had this reproduce with 2 users today, so I'm assuming this is fairly straight forward to reproduce.
1. Add some users and generate welcome emails
2. Have those users be really lazy and not click on the link in the email for a while.
3. Once they do they're given a message about how the link has expired and they need to request a new one.
4. Clicking the only button on the page results in 404 error.