I have mfp, runkeeper, and fitbit also. runkeeper and fitbit are close, but the caloric burn is off. i find that even though i've shaved a min off of my average pace, it still says a moderate pace of 3.0mph. I have no idea WHY its doing this... but i know that the post is being fed to mfp through runkeeper, not through fitbit. i have all three synced, but i dont think that runkeeper is affecting my fitbit data. what i see happening is that fitbit syncs to mfp and adjusts the calories... i think. i have went round and round with fitbit about this and unfortunately, because all three have different web-developers, there isnt really a "fix". they all use variations of the same calculations and different software to pull their data, so it's not going to ever be completely cohesive. i also use mfp as my "hub". i basically use fitbit to keep me in check throughout the day, runkeeper to track my runs, and mfp as an overall information-board, as well as the place i store my food and focus on my caloric in vs. out.

While this doesnt answer your question, at least you know your not the only one with this issue. i have posted threads about this before when i first started and talked with people who have been using these apps together for years... and there is still no fix.