There are many theories as to the reason for this but I think you probably just want it to stop.
1. Pick up the poop immediately whenever possible.
2. Supervise the pup and take it out, don't just let it out to do it's business.
3. Start teaching a "leave it" command.
4. There are many things including pineapple, meat tenderizer and special food additives you can buy or get from your vet that can help prevent the poop eating by generally making the poop taste bad to the dog. Personally I've had the most success with adding a bit of plain canned pumpkin (NOT the pie mix) to a dog's food.