Since both the 'Login' and the 'Create an account' links on the site point to the legit poloniex.com links I think this site belongs to the legit poloniex exactly to avoid the domain to be used for phising.
I hope so, but I would guess it says invalid, then returns you to the normal page, even if it's correct, just to gather data. You would then try logging in again and be logged in fine, thinking nothing is wrong
Yeah that's what I was thinking, a prime example of phishing.