I was called into one of our academic computer labs with Macintosh computers setup with LDAP for students to login to the computers. Fast user switching was turned on. When another student tried using the computer with their credentials the pop up client would only show up on the previous student's login and so the second student would not be able to print unless the computer was rebooted to quit out of the login session of the first student. The take away from this was that fast user switching is a bad idea and needs to be turned off. When we disabled fast user switching this either forced the first user to log off or the lab manager to log off for them and so the pop up client only ran on the currently logged in user. Hope this helps any one in a public computer lab situation using Macintosh computers running OS X.