Garmin Vivosmart Double Counting Active Calories

I recently switched from using a Fitbit Flex to a Garmin Vivosmart. I am concerned that the Vivosmart is double counting my active calories with steps and an activity.

I am rather out of shape so walking is enough to get me unto Zone 3, and sometimes Zone 4 if I get to more of a speed walk. I have my Vivosmart paired with a HRM and use it during walking workouts.

Maybe it is just the way Garmin Connect, and the synced workouts are listed in MFP, but I think my steps are getting double counted.

Today I had a morning walk for 20 minutes worth 144 calories, in the evening I walked again but at a faster pace so it was worth 214 calories. I work a desk job so for most of the rest of the day I was sitting. However, Garmin still gives me another 583 calories for my steps. Bringing me for a total of 871 exercise calories.

This seems like a lot for a day I mostly sat on my butt.

Thoughts? Should I trust the adjustments Garmin is giving me? I went back to a similar day when I was using a Fitbit Flex and it only gave me 290 calories for the same morning/evening walks and my day at work.