Issue logging in with username/password after registering with GitHub

To reproduce:

1. Register with GitHub
2. Provide a username
3. Log out
4. Go to login
5. Do forgot password flow
6. Click link in email to reset password
7. Reset password, using username entered in 2
8. Try to log in with username and password
9. Cannot log in ('Found some problems! Incorrect Username or Password')

Not sure if this flow should even be possible, but then I probably shouldn't have received the password reset email in the first place, right?

Start by reproducing the numbered registration, password-reset, and login flow described in the issue. Then inspect the corresponding authentication paths to determine whether GitHub-registered users should receive password resets and be able to log in with the supplied username; done means the supported behavior is consistent and the error no longer contradicts it.

Written by the indexing model from the issue text.