I have just set up an additional sub account @xtra.co.nz email address. It was the first time it had been used and Yahoo asked me my name etc, but when it comes to the "You're almost done" page, when I click finish it redirects me to the Yahoo homepage. Every time I do log in I get the same "You're almost done" page.
If I try and setup the new email address on my iPhone it asks me to complete verification - which I can't do because I can't sign in. Argghhh.
Screenshot below is from the final step of the add account phase, but also pops up when I try and sign in as the new mail user. It's as though it never quite completes the wizard properly....