It's not really a bug.
The kerb is not part of the race track. The race track is between the white lines. You should keep four wheels between them at all times, strictly speaking, although the accepted norm in LFS is 2 wheels on the track.
You can see clearly from the picture that the kerb is a couple of inches higher than the green concrete inside it. If you spin there (like I did going the other way in OWRL if you recall Ramon) you have gone over the kerb and have the tyre on the concrete and catching the ridge can spin the car.
Solution - don't cut the track.