That is common to the yorkie breed I believe. At least I've never seen it as common in other breeds! Yorkies seem to be pacing poopers.
Coby started that, but we tried to solve it by either keeping him on the leash while potty training (so we limited him being able to "leave" the pad) or else fencing him in to just the potty pad area while he pottied. It seemed to create his pacing habits to be circles (on the pad) instead of straight lines (right off the pad).
Don't know if that really helped or if we were just lucky. But Coby does really well (unless he's having one of those "problem poops"
)