Dave,
I don't have any of those AI packs that you mention so I probably should be

but I have noticed the same thing at EGJJ. I think it is the AFCAD that is at fault and I have tried more than one. Actually I suppose it is the airport layout because there is only one route to the gates and parking at the rear of the terminal. Looks to me that in FS, if a plane has landed (especially on runway 09) and gets ATC instructions to parking or a gate in the rear of the terminal, it can be quite a time until it reaches that curve that takes it around to the back. In the meantime ATC has cleared another plane for taxi to takeoff and the two meet at that bottleneck. Hmm, that probably means it is not the AFCAD but the FS ATC logic, since in reality one of the aircraft would be held until the other was clear of the bottleneck. Now at many airports in FS that actually happens, ATC works as it should and you are held while another taxiing plane clears, but at Jersey it does not for some reason.
One possible solution is to change times for one of the aircraft so there is a gap between arrival of the first plane and departure of the second. Even that technique may not work all the time because when FS is first started, the planes that are scheduled to leave an airport for the
past 15 minutes or so, all ask ATC to leave one right after the other. Also arriving planes can be delayed for go-arounds and so on. Forgive me if I have misunderstood the problem. :prayer:
All that said, I just pretend there has been a tear in the time continuum and when a plane dissapears, and it has been teleported to another dimension. Saves a lot of bother. ;-)