I'm trying to put the Exmouth Exodus in, but there are places on the route where officially it's no through road/left turn only (or whatever) but you can sneak across on a bike. This plays havoc with the routing. Sometimes it's just plain wrong and makes you do a U-turn and go the long way round for no apparent reason. The best thing to do is review the route, note where the routing fouls up and just ignore it at those one or two points, carrying straight ahead whenever it tells you to do a U-turn.
Those on the FNRttS may remember it getting upset when we crossed the Oxford southern bypass, because it's not possible by car at that point. Of course, the moment you're through and it gets a whiff of the next waypoint, it's happy again.