I have been tracking down a bug for what feels like an eternity... I think it lands here.
Using the Commerce Checkout Redirect AND Email Registration module causes the user to be emailed twice about the registration and their account is mangled. First the Email Registration module creates the user and assigns the username -- then something else does.
I do not have a huge knowledge of the code side of drupal and was hoping someone might be able to recognize the problem here.
I have attached two images, one of the double email (showing how the username is mangled) and one of the watchdog logs showing a similar event.