Negative calorie adjustment my fitness pal

Hi, 

New to garmin, just got myself a venu. I don't understand the connection to mfp. I wore the venu all day long, took a walk and went to the gym for a workout where according to garmin connect I burnt some 495 calories.

I have integrated it with mfp where my goal is on 1200 calories for weight loss. Today, I ate thus far 900 calories. For the exercise that comes from connect, mfp gives me those 495 calories but subtracts 310 for "negative calorie adjustment" and 11950 steps. 

On connect however, it tells me I have 860 calories left to eat. 

What is going on there? I don't understand a) why the number of calories I have left to eat is different and b) why I get only 185 (495-310) calories for my workout today. Feels a little unfair

Thanks and best, 

Scw