In practice, it seems doesn't matter...
Just thought if it was an easy things to consider it, so it's just a suggestion sir :)
But One of my users reported to me for some strange thing (I've never seen it my self)
He said, He logged in with his user and password, after clicking on enter, another user and password were logged in, (other user of forum).
I didn't understand how could it happen, but maybe from the Anti-Filtering softwares like (UltraSurf or...) if two person has same program, but how can it be? Does it happen for you or any one else? if so how it could be and what's the problem?