@acidduk: Thanks for uploading, that really was helpful! The problem is that in the vicinity of wind turbines you don't really have an "all open/empty concrete" area because Nullius places some hidden entities with a huge collision_box.
GCKI will check whether a vehicle can be placed at the selected position, first using player.surface.can_place_entity (so that we don't try to place a car on water etc.). In the last version, I added another test that will be run if the first has succeeded -- checking whether the vehicle would collide with another entity in its current orientation (can_place_entity only looks for collisions when the vehicle points northwards). It seems it's not enough to look for just any entitiy, but to check its collision mask as well. Shouldn't be too hard to fix now that I know what's wrong. :-)
Also, I noticed that there are still records of vehicles that you once must have locked but which don't exist anymore in the global table. I'll try to fix that as well for the next update.
