Hey I just had to put in my thoughts, I have dog with the same problem, I think it is a discusting habit. A few years ago we bought an older dog, she came with this habit and unfortunately tought our then puppy. In the mean time she has passed, and now our puppy, who is 1 1/2 is teaching that habit to our new puppy, 6 months. None of our other dogs do or did this, untill we brought home that one dog, and then it is only the puppies who are influenced. The new older dog we bought a year ago does not do this, they are all on the same food, except the puppy, it is a high quality chicken and rice food. I can not tell who's poop the dogs are eating, since we are on 2 acres and they often go out of sight to do their "business". I think it is just a habit because they have also taken a liking to racoon "bisquits" and used to eat cow "patties" when we were on the farm. It is just another gross thing dogs do to amuse themselves.
I heard that there is something you can add to the food that will make the poop tast bad (like it doesnt already) and discourages them from eating it. I will be looking for it in the petstores near me.
A well behaved dog will never steal your lunch, he will just make you feel so guilty that you can't enjoy it. - unknown