Several months ago on our way to Reno I was swearing at the Nav near Seattle for trying to take us off I-5 S onto the 405, which is a longer route. Couldn't understand why it would do that, there was no reason to. Until a mile or two down the road, and we hit (not literally) the I-5 Parking Lot. I was quite impressed at that point, and [almost] felt a little guilty for my blue language earlier.
My solution to the "go back to the last SC" problem is, since we have our route planned out anyway, to just input the specific next destination, which is either the next planned SC stop, a side route for pleasure/exploring, or our hotel for the night. Only occasionally do I have to ignore the crazy rubber banded last SC directions.