MFP, Fitbit and eating back calories

Both my Fitbit and MFP are set to sedentary and each has given me a 1200 calorie goal per day. i eat back most of the exercise calories that MFP gives me and except for a couple of days, MFP shows that I am under my goal of 1200 + exercise. On the other hand, if I eat over 1200 calories, Fitbit indicates that I did not meet my calorie goal for the day. To experiment, I decided to eat only 1200 calories and not eat any of my exercise calories. FItbit was fine and said I met my calorie goals for the day, but last night, MFP wouldn't let me log out until I ate some of my exercise calories back. (I ate a tablespoon of peanut butter. What could be happening?