"Calories burned" vs Work (kJ)


for many years the calories and kJ (mechanical work) count for me were almost identical for bike rides with power meter readings. In other words, Garmin used the traditional 1 kcal = 1 kJ. 

Now since a few days I get completely different readings, with significantly more calories burned than mechanical work (kJ). 

Does Garmin Connect add basic metabolic rate to the active burned calories, or does it estimate a lower mechanical efficiency?

I have a Garmin 1030 and pedal based powermeter, but I see the same for my friends too.