I'm not sure if this qualifies as bug but if you add command '/press 3' (turn on lights) to any CAR.lfs script then it will not turn on the lights if you leave pits from garage. However, it does work if:

-you join track from spectator mode
-reset car
-restart race or start race from lobby (if your car is on track obviously)

So it seems that upon leaving pits from garage the script is executed before the car is "ready". Tested with 0.6V and 0.6W43.