I think it is software bug and been trying to communicate to Apple support and failed. My watch records active calories 4 per minute. Apple says it is calorie burned living. Yes, but it is not active calorie.
Total calorie = Active calorie + daily living calory
In normal conditions or while doing outdoor activities, it logs active calorie correctly when above resting heart rate.
But when you select any indoor work out, it logs daly calorie in to active calorie too even if the watch is resting on table! During workout only active calories should be logged.
When you do work out you actual calorie burn is = Active calorie - (Time * 4) This will reduce resting heart rate being added.