The only way I can explain this is if the actual route data is going past the turn and then approaches it from the other side.

Hmmm, good point. Perhaps the map data has some extra fiddly bits, very small (i.e., not visible at regular zoom levels), right at the turn intersection. Maybe the problem is still the map data itself. I will investigate this.

This was done with old map data from MapsOnUs, which we all know isn't necessarily the best. Perhaps the new data using FromSA will be better and not have this problem. I will try it.