Not sure where to ask this as this relates to add-on aircraft designed and distributed freely to the FS community. I 'fly' from a busy airport with about 60% of the GA ramps in use. On most occasions when I 'fire-up' there are a few Piper Cubs and a Stinson Voyager on the apron. After a few seconds some start moving and just drive off into the distance although some occasionally stop. Another strange behaviour is that the Cub when 'started' seems to lose it's route and wanders aimlessly around in circles for a bit, then taxies out and takes off normally. I have no circular apron routes. Also the Stinson sometimes sits on the apron horizontal rather than tailwheel down, but stationary. Have not a clue where to look as aircraft.cfg files seem to be OK although accuracy of the data therein cannot be checked. Any ideas.