Thats because a tail stall happens more readily during icing situations. It is for that reason many aircraft have a lower flap setting used for icing conditions to reduce the disrupted flow over the tail. Too bad those folks hadn't taken a class on that, or had the experience.

As for inaccuracies, I can only speculate, but I would assume if they developed the system those inaccuracies would and could be accounted for.