Problem with splines

A few months ago I created a route in TS12 (no SP1) with several towns and cities. After running a few sessions on the route, I decided to add a couple of dirt road splines to the route. After adding the splines with no problems, I saved and closed. When I came back to run a session on the route, the dirt road splines where scattered everywhere on the route. The splines were connected to rail splines and invisible splines. It is easy enough to delete the unwanted splines but when I go back to add the splines I want, the same problem reappears. I have been careful to add new assets at the route level. Anybody have any ideas what causes this annoying problem and how can it be prevented?
Thanks for any input.
Gary

This problem has been posted too many times already. The good news is that you are experiencing the same thing that many of us. And the bad is that N3V knows about it and so far is mute to bring a solution or even advise. Here is what I do: I clean the area I am modifying of any nearby spline ( do this is session). Then add the spline you want in route. Now go to session and see if it is there. That way everything should be alright. If you see tangled or running to infinite splines, insert a spline point near the origin, and delete the section that goes nowhere. Reconnect the spline to where it should go and take a look if it is OK. Problem is that the route will not be modified doing this. You may have to go several times from route to session until you get it right. A hassle? You bet! If you try to install an animated turnout, using invisible track and all that, be prepared to spend about 10 minutes on each going back and forth (that is with experience) Now it is not a hassle, is a bummer!

Thanks llebrez. I didn't realize this problem had been posted many times before. I will try your suggestion.
Gary