Forerunner 945 and the Cardio setting.

Has anyone else noticed a problem with the Forerunnre 945 using Cardio training.I get average  heart rates exceding 185 walking arount the lounge room. My 12K run gives an accurate heart rate average of around 135. Ridiculously high levels on the Cardio setting. I am suspecting a software bug when using the Garmin Cardio activity.