The Management Console will shuffle guys to inactive if they fall below the threshold that you set. It will activate another guy in his place.
But if you have a guy that's been inactivated, there's no assurance that the Mgmt Console will later select him to reactivate during a future inactivation. So it's probably working the way it's designed to work, but not the way that you want it to work.
It would be nice if there was an option to designate guys as "keep active when above threshold".