This is something I don't like about MFP! It encourages you to "eat back" the cals burned.
I work at a computer all day so I put my activity level as "sedentary." I do log my exercise, but only for the minutes, not the calories. I don't try to "eat back" the calories burned unless it's a super hard workout (running for 45 mins+) and I want to add in an extra 100-200. I never try to eat all the way up to the goal they give me by adding in my exercise cals.
This is just what I do, I try to be conservative about assuming the number of calories burned each day, to be on the safe side