So the controller gets accustomed to pilots adding that extra information when cleared for the option but planning a full-stop then someone else comes in and does it by the book and the controller is caught off guard. Maybe he even scolds the pilots over the frequency as was reported above. That is negative training. The "good idea" has replaced the standard procedure in the minds of many while others continue to use the standard.
Same kind of thing with "downwind abeam" report. "Abeam" isn't a location. It's like saying "over" or "behind". It can describe a position RELATIVE to something else. If the leave out the something else, as luvflyin did above, it is meaningless. Is it downwind abeam the tower, abeam midfield, abeam the approach end, abeam the departure end, or abeam what? Controllers at a particular airport might be in the habit of having pattern traffic report downwind abeam [insert local landmark] and pilots and controllers at that airport may have slipped into the habit of shortening that to "downwind abeam" but non-local pilots won't know that. People reading forum posts won't know that. Pilots at a different airport won't know that (and may have their own, different, commonly used "abeam" point).
My bigger point is to avoid "local" or "individual" procedures in favor of the established standards. The system works much better when everyone, and every airport, isn't making up their own practices.