The Setting for unanswered calls resets every time the user sets the call forwarding to a Special Destination.
1. User has no voicemail enabled
2. User sets destination for unanswered calls to the central office number
3. Now, the user sets a call forwarding to a colleague
4. After disabling the call forwarding, the konfig for unanswered calls resets to "no voicemail, ringing for 20 seconds.