Strange you can't post in the support forum for FREE addons!. Anyhoo.

Great feature, but with a small problem that may have wider consequences.

When a user signs up with their Twitter account, it puts a unique ID into the e-mail address. This means that the user cannot be edited in the dashboard since you get an "Invalid E-Mail Address" error. Additionally, they cannot sign in via the regular sign in page if the site is set to "Use Email Address For Sign In".

I haven't checked, but this presumably would also be an issue for automagic e-mails or "Forgotten Password" requests.