I've just opened PH and found myself logged in as a different username (stevez from memmory). F5 (refresh page) logged me in as my own username. No problem for me, but I tought the great people who manage the site would like to know.
As Phil says, it is an ongoing problem which we are still working on.
If it happens again then please do let us know on the main thread, including both the page it happened on and the page you were on immediately beforehand.