In the loop around line 1490 ("Loop over all the objects we found and find the first vehicle") it may be a good idea to add a check for v.prototype.selectable_in_game. If a car is not selectable, then it's probably not a "real" car and may be some kind of mod-related fake car.

Thanks! I'm now building a list of the prototypes GCKI should handle the first time an event from defines.events is run after starting/loading a game. This requires some magic from Eradicator's L.I.B.R.A.R.Y.), so I've added a dependency on it. The prototypes that are selectable_in_game will be put in this list, unless they have been explicitly blacklisted. Prototypes that are not selectable_in_game will be added if they've been explicitly whitelisted. (I still need an elegant way for other mods to black-/whitelist their prototypes just during the data stage, not in data and control. For now, the lists are still hard-coded.)

Added in version 1.1.2. Thanks again for the hint! :-)