Maybe most of the blame.

But consider this: If a human had the same problem, who would be blamed? If several humans, then the road would be changed, just like this. The process seems sound, but maybe the changes that make it more human-friendly make it more machine-hostile.

New thinking is needed on how we retrain machines after the change, as it necessitates uniformity - the machine would benefit with fewer variations in cattle grids for example. I reckon a simple change to the road markings for all cattle grids would be enough to make them logically identical - be it paint or signs or some other physical indicator.