Well, you will see a timer for any busy member when its on a call, and the timer will clear when the call is done. This is based on AgentConnect/AgentComplete events, so they must be present in your manager events for them to work correctly. If one complete even is missed for any reason, a timer might continue counting even if the call is done. It is hard to tell as events are that: events. And they usually cannot be replicated in the same way/scenario every time.
Be sure you have a manager user with full privileges, and eventfilters in place, as documented in here:
www.fop2.com/docs/#ConfiguringtheServer
Best regards,