Hi KDubya, welcome to the community.
The PC icon should be Blue when the computer is available and Green when it is in a session. This doesn't appear to be an issue that support has heard of already, so would it be possible for you to call in so we can gather some more details and log files from some of the affected computers?
It is possible to block another user from connecting while a session is in progress if you use the Host Preference Package feature. Once you create a package, in the Advanced section you can uncheck this box before deploying it.
