When you register on xat using the xat app (tested on android your guys can try on iOS)... you will choose your username, password, and email then complete captcha
But when you receive the email, your username will be empty, but if you do login using your email, you will see that the username is something like "xat123456" where 123456 is your ID
But, I don't think is correct allowing users to register using "xat" on username, so, it's a bug.
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