Quite obviously, Google does not always get it right either. Ever when I try to see my Google Calendar (using Opera), I am requested to login. So I enter my credentials, am redirected a couple of times and — are broght to the login page again. Logging in again does not help, I have by then entered an infinite loop. Thankfully, I can escape this loop by jumping to the original calendar URL again — now Google recognizes that I have already logged in and shows me my calendar. Great.
But this one is even better. Having received an invitation, I was presented with a page offering me to accept or reject the event.
Look at the screenshot — you can select all three options Yes, No and Maybe at the same time! Very convenient indeed. Having submitted the form, this answer seems to have been recognized as a Yes. Amazing.