It's possible to get the error in the screenshot (flash of "you're successfully logged in") if you end up redirected from the login page back to the login page.
The steps I used to reproduce this were:
- Hit a protected URL with an invalid session (get redirected to login page)
- Walk away, get coffee, lunch, punch a seagull or something like that
- Return and try to use the same form (no page reloads) to log in.
- See the error page of "you spent too much time on the login page" (side note: that's silly)
- Attempt to login again successfully
- Find yourself redirected to the view in the screenshot