It does this same thing when you're trying to use a road that parallels the main highway. Sometimes I don't want to go 70, I want to go 45 on a nice quiet side road. Well even after I programmed a specific route, it keeps trying to take me back to the main highway because it found a faster route. Fuck, I don't always want the fastest route. I basically don't use any turn by turn navigation stuff anymore. I check routes before leaving, take a few notes on a piece of paper, and memorize it. Not only do you learn the route much better, you have much less chance of getting lost, and you're not constantly distracted by your navigation app.