I am running Adium 1.5.7, SIPE plugin 1.16.1, on Mac OS X 10.8.4.
I am connecting to a corporate Microsoft Office Communicator network server.
When I set my status to any "away" or "busy" status, other users connected to the network see that my account is "offline". I don't believe this was always this way, but must have happened with some recent upgrade. (It was broken in 1.16.0 however, as I just upgraded to 1.16.1 today in a vain hope it would fix the problem.)
In the attached debug log, you can see it connects and logs in with "away" status, and sends the server the signal to go invisible. I then change the status to Available, and am no longer invisible. I then switch back to Away and turn invisible.