This is indeed a nastly habit, but it can be corrected, and it isn't just the Yorkie breed that does this, but does seem to be most small breeds.
If what your giving doesn't work, then try a different brand. There are many on the market. I have a Papillon and a Shi-Tzu/Maltese mix that like poop and since I started giving them and my three Yorkies Forbid , it has stopped. I don't like giving my girls things like this, but at the same time I don't want Spicy and Belle eating poop either.
FOR-BID Stool-eating preventative (12 packets)