Ever since "upgrading" to 10.5.4 yesterday, fast user switching has been having problems. Randomly, when I change to another account (all are password protected), it will just instantly log me out, without even trying to close apps etc. - it literally takes it a second to log out, then I have to go back in and log in from scratch. Normally, it keeps everyone logged in, with the orange tick beside logged-in users (it logs me out, then the tick goes). Sometimes it's OK, sometimes this happens. Has anyone been having the same problem?