Thanks for the saved game! I know now what went wrong!
Looks like the triggering condition is havign a gate sensor in the grid
Actually, that's just one thing that may trigger this. It would happen when the vehicle needs to have a driver or passenger, which is true if a vehicle following a path has a gate sensor, or if it has an enemy sensor and guns with ammo and needs a shooter because it has detected enemies within range of its weapons.
Up to version 1.1.12, we'd check vehicle.get_driver() and vehicle.get_passenger() on each tick to find out whether a dummy must be inserted. In 1.1.13, I've changed this to storing the list of occupants with the vehicle state whenever on_player_driving_changed_state was raised. However, that list wouldn't be preserved when a vehicle was reset (e.g. when it had arrived at its destination).
So, with versions >=1.1.13, the first time a path was set for the vehicle, everything would be normal: If there was neither a driver nor a passenger, a dummy would be created and put in the passenger seat. When the vehicle arrived, the dummy would still be passenger, but as there was no record of it, another dummy would be put in the passenger seat the next time the vehicle was following a path, and the existing dummy would be ejected.
As a quick fix before I can upload the next version, try adding
state.occupants = common_vehicle.get_players_inside(vehicle)
at line 576 of scripts/vehicle_functions.lua (directly after state = mod.vehicles[state.id]).
EDIT: Sorry, made a mistake! I've renamed the function for the new version, so common_vehicle.get_occupants wasn't correct. Use common_vehicle.get_players_inside when you fix this for version 1.1.13!
