OK, couldn't try it on my drive home from work because my Nav chose to continue not cooperating. Rebooted when I got home. Ran some errands later and Nav appeared to be working so I turned them on for the errands. Also left them on for my drive in to work this morning. Again, not sure how they are supposed to (or used to) behave. They were appearing on my map but they certainly didn't stay there. I wouldn't even say it was a couple of miles worth of distance before they disappeared, more like half a mile. Seems kind of useless for backtracking unless you only want to backtrack a very short distance.
.......here's a lockpick. It might come in handy if you, the master of unlocking, take it with you.