Well that might be just what solved My problem, still not sure it has solved Keal's problem from which I so bluntly stole the thread , Sorry.If you start putting FS2002 type AI Planes into FS9/FSX, the rules have changed and you must code a Pushback into your XML which is basically the same as the txt code previously used.
Thanks for your explanations, and yes I have a Hold-short as my AI just continues to taxi out on the RWY and then halt's there if I haven't ;-)
Anyway, others than me I think will be using models from various versions of FS, especially if you have the need for using a bit rare aircraft and none new version is available.
So all I can say, is that in my particular problem, with my particular aircraft, it solved the vanishing by adding other than NONE into the PushBack property ;-)
As you say, that might be backwards-almost-compatibility-reasons then...
But it works for me, so I'm a happy bunny. Good to have those other things in mind though.