How does your GPS handle navigation on non-roads?

For the models that route you along roads, how does yours handle situations where you are traveling on roads that the GPS database doesn’t know about (or when you are taking a a off road ‘shortcut’)?

I’ve not encountered this situation for anextended length of time, but when driving off-road (e.g. across a campsite) it generally just draws a straight line between my current position and the nearest bit of road. Plus, when you get near enough to a road it tends to “snap” your position onto the road and assume you are actually on it.

“Please return to the indicated route.”
Plus on some factory systems, if you make too many turns off road (a big parking structure for example) the system may get confused, and the map will tumble. The map will just turn over and over, like a passenger is holding a paper map and rotating it trying to find where you are. Shutting the system off and restarting it will restore normal operation.

I have a Tom Tom. The screen shows my location accurately (looks like I’m proceeding through a field or something). The voice directions usually tell me to turn around for a while, then it gives up.

My Garmin Nuvi usually doesn’t have any problem with large parking lots or whatever. It just shows me in white space and a says “Please drive to highlighted route.” (I have the GPS voice set to Australian female, just because it sounds so damn sexy).

Everyone once in a while, though, it will go crazy (show me driving the opposite direction of where I’m actually going, or whatever), and I’ll need to reboot it, but this is pretty rare.

Chrysler’s “REC” system (built by Alpine, mapping by Navteq) will bug me about being off the prescribed route, but otherwise, it will gamely show my position in the middle of nowhere and say “Please proceed to the highlighted route” once it figures out what road will get me back on the way.

I’ve never managed to get it so muddled in a parking ramp or middle of nowhere that it went into “Help! Mr. Wizard!” mode and started spinning endlessly.