Fit Bit Calorie Adjustment

I have my Fit Bit One synced to my account and it automatically adds "exercise" calories throughout the day depending on my activity level. My question comes about after I log an actual exercise/calories burned from my heart rate monitor. MFP will log those calories burned and then take away all or some of the fit bit burns (which I understand due to the formula they use to calculate all this) BUT then moments later my calories burned from the fit bit will jump back up. That I don't understand. Why take them away only to add them back a minute later? Anyone else noticing this? Is it correct? Just want to know since I tend to eat back a lot of my exercise calories. Thanks!