That's because the login username and password fields are to the left of the Login button. If you've not filled them in, pressing Login is a failed attempt cos there is no username and password being submitted.
I've possibly changed the colours of the boxes so you didn't realise the data entry boxes were there - I'll take a look.
It happens to me, however if I click on the NSC banner I'm suddenly logged in again. (Mac user)
Its a small price to pay considering the many other benefits of Mac usage, the women, the large penis and the fast car.
Oh yes, And my penis was tiny before I went 'Mac'.
Sounds like an advert for McDonalds