My understanding is that the train software got built, more-or-less, according to the spec given, in a synthetic environment. The problem is that in real-world

My understanding is that the train software got built, more-or-less, according to the spec given, in a synthetic environment. The problem is that in real-world testing, conditions around the changeover points produced behaviour that was not addressed by the spec. It turns out that dealing with radio-based systems in the middle of a busy rail network in the middle of a city is really hard. Many of the problems were caused by radio interference in the area. It's definitely the sort of problem practically nobody on this forum works on.