The problem you describe is probably not caused by UT but by a faulty AFCAD. If you do not have the AFCAD tool by Lee Swordy (available from avsim) get it, open the airport you noticed disappearing aircraft, click on "Tools -> Fault finder" and run it. If it does not find faults come back here and I'll try to help you further. On the other hand - I just reread your post. Are you talking about waiting in queue before takeoff? And some aircraft waiting with you disappear suddenly? If this is the case the aircraft waited longer than 5 minutes. There is a tool out there that you can use to exceed this time given by Microsoft. But I do not use it so I dunno the name of.
The planes move around as if they were piloted by a human. Well, at least some kind of - Microsoft has some restrictions. WoAI aircraft follow real world flightplans. This means if an airport is closed at night you won't see any aircraft ops. But if you have a summer 2008 timetable of an airline you got a summer 2008 WoAI pack for you can check if their aircraft are on time
