Dropped Route Sections
Nick, the only times that I have had dropped maps or sections of routes is when I haven't used a lot of waypoints to define the route.
Maybe Crafty can shed more light on it but as I understand the way the app/website interface works, if you auto download the maps along a route, but there are no waypoints on a particular map tile (the maps are not down loaded wholesale, they are downloaded in fairly small sections, "tiles") it won't pick up that particular tile. Conversely, if you manually download a map but there are no waypoints on the tiles you choose, it won't bring the route along with it. I'm not a code writer so I can't know if that is totally the issue, but it might be worth trying to add some more waypoints to a route and see if that changes the results when you download.
It really is a great app. Good luck!
For what it's worth, as long as I have defined a route, I use it for street nav all the time (or just to display my current location and the map of the area). But you're right, the routing function is fairly weak as that's not what Crafty intended it to be for. If I need to find directions from here to there by surface streets, I just fire up google maps and let-er-rip.