It's an ever present problem. Sounds like you were taught to fly properly. Unfortunately, others seem to be taught by those who fly a circuit more like a navex.
A colleague of mine was once phoned up by an irate instructor, complaining that he had "cut in front" of him and his student, as they were turning base leg in "his" circuit.
However, my colleague was on our company instrument approach, directly overhead the NDB, in the overhead of the adjacent airfield!
Not only was the instructor allowing his student to fly completely outside his own ATZ, he had gone five miles downwind, penetrated another ATZ and contravened someone else's circuit pattern without obtaining clearance. Idiot.