Garmin confused while calculating, shuts off?

I mapped out a ride on mapmyride.com, which included a section of road and the C & O Canal Towpath. I then uploaded the ride into the saved rides folder on my Edge 705. As I scrolled through the cue sheet, I noticed that the Garmin didn't really know what to do with the Towpath (it not being a street. I have city nav on a card in the unit). Didn't figure it was a big deal. The cue screen just kind of skipped it until the next street after the 12 mile Towpath section.

Anyway, once I actually got on the Towpath, about 17 miles into the ride, the unit attempted to recalculate. Obviously it got confused, but instead of coming up with an error saying it could not navigate or something, it just turned off. I turned it back on, and everything seemed normal at first. I did not try to renavigate the route (it's a straight shot on the Towpath. If I needed it after I got back on the road, I could renavigate then). I then noticed that my average speed had jumped up a couple miles an hour. huh? It appears that it somehow dropped some of the elapsed time off, but not the mileage.

Anyway, I thought it was kind of weird. Anyone experienced something similar with their 705?