I had a similar thing happen on 0.14 this morning, and without any ignition on/off intervention.

GPSapp was tracking my progress on the selected route. But I exited out of GPSapp for a while (GPSapp still runs I think, just doesn't grab the screen). I went back into GPSapp and it was still tracking correctly with the right map, but twiddling the knob to change waypoints did not work. It was almost like the processor was busy doing something more important than responding to my knob commands. So I exited out of GPSapp and tried to go back in again and it was gone.