Thanks for that....
I suppose that looked like a silly question.....
but the unassignvehicle command in the command ref really didn't give that much of I clue. I should have tried it - i was looking for unassignascargo...but never mind.
I don't know the form here but Ill take a few seconds to write up this topic incase you want to move it to the snippets section via a cut and paste.
...
Units starting in vehicles in the 'in cargo' state need to be removed from that vehicle.
simply
unassign vehicle unitname
If you forget this units will tend to get back into the vehicles they were just in rather than follow waypoints.