Possible security glitch with switching users?

All, I don't know whether this is a security glitch or PEBKAC. I was testing the graphical login with TDM: * I logged in as User 1. * From the TDE menu I selected Switch User->Start New Session. * I logged in as User 2. * I switched to User 1 *without* needing a password. * I switched to User 2 and needed a password. * I typed the password, switched to User 1, and needed a password. I repeated this exercise three times with a system reboot each time. Each time the first instance of switching did not require a password. Further, I was not always asked for a password on subsequent switching, especially when I used the keyboard toggles of Ctrl-Alt- F7 and Ctrl-Alt-F8. SAK is disabled. I only used Switch User->Start New Session. I did not use Switch User->Lock Current & Start New Session. Thoughts? Darrell