Also because user was registred/Logged in with SSO
In Profile password fields are disabled, but user still can change username or email without entering a password (strange)
I've also posted an issue with Usernames editing on Github
Strange behavior when "change usernames" is disabled
I would also like something like this for other reasons. We have a sub category where users post questions and we have certain people assigned to receive emails when new topics are posted - they are supposed to then go and reply to the question and it would be nice to be able inform them somehow that someone else (that was emailed) is already in the process of replying.