Could have tested it this evening since I work from home, but I'll try it tomorrow morning and report my findings. lol
There is a ''timer'' that you can set your statuses to let people know you're away, on vacation, etc..and it appears as though available is an option for the timer, as well. But, you need to add a message to your status, then set it to ''never'' where it asks when you want the message to expire. For some reason Seattle, it doesn't work. After a few minutes, nearly every time, it would show my status as ''away.'' It's not like the sky is falling when this happens, but it's annoying considering...I'm not away.
But, Neddy solved the mystery ...the status changes seem to coincide with Outlook usage.