This has been the way it has always worked but they did make some changes to that process recently - it may have been in one of the HF1 betas ??? (its late and its been a busy day).
If you are just changing the route (e.g. editing textures, landforms, and the contents of the route layers) then select the option to not save the session when you save. If you are working with a session then always make sure that the session is given a meaningful name (not default) and from then on, always load and edit the session not the route.