In a way it is by design. The 'turn' information is not stored in the route files, but generated on the fly by calculating the difference between the incoming and outgoing heading of a turn. This is stable for all points except for one, which is the turn we're approaching. This is because the code assumes that our existing location is more precise and if we were to approach a turn from the wrong direction after a short 'detour', the instructions will still be right.

It bugged me when it was telling me to take a right onto fifth avenue when I knew it should be a left because I had selected a route with a different startpoint but the same endpoint as where I was going to.