I have the same problem. One of my users who never had admin access shows up as admin quite often in the logs and the now playing tab. This happened in 4.3, but its much more often in 4.4 now. Also its not just one user, sometimes others are affected too and show up as another user.
This one user that often shows up as admin has never shared a browser or pc with the admin account. Other users do however, maybe this mess of cookies and sessions tilts SS's session management...
EDIT: if something is amiss in the "now playing" tab like showing wrong user/different user than the log, I just issue a "cookie/cache extermination signal" to my users via chat. And most of the times this works. But its a solution unbefitting to SS really
