I'd say it is a big that is stores username in the email field.
It should use a 'username' field.
I will look into this but for now my suggestion is edit tools and
change
if 'username' in table_user.fields:
username = 'username'
tmpvalidator = IS_NOT_EMPTY(self.messages.is_empty)
else:
username = 'email'
tmpvalidator = IS_EMAIL(self.messages.invalid_email)
into this
username = 'email'
tmpvalidator = IS_EMAIL(self.messages.invalid_email)
Sorry for this problem.