I think your Garmin must be playing up - I get about 11.4km for the full red loop using my Garmin! And I know others who get about 11.8km with a speedo that doesn't use GPS. (I'm still not convinced that the GPS units account for all the small ups and downs all that well!)Revising myself down:
I measured the track with my Garmin yesterday and it was more like 8.5 km in total - not sure if my Garmin was playing up.