A Boeing 737 was cleared for take-off from runway 23 but was instructed to stop by the Tower controller because a Piper Seminole had inadvertently infringed the upwind end of runway 23 at 1000 ft AGL. The 737 had come to rest at the runway 12/23 intersection. During this sequence of events, a Saab 340 was on final for runway 12 and was instructed by the Tower controller to go around because the 737 was occupying the runway 12/23 intersection. The Seminole had been cleared by the Tower controller to track for a left base runway 23. The pilot of the Seminole had inadvertently tracked for a right base runway 23 which brought the aircraft into potential conflict with the projected take-off profile of the 737. There was no breakdown in separation. When the Seminole pilot was instructed to turn inland, he thought that he was required to turn inland from the coast and then continue to track North across the extended runway 23 centreline to then join a right base for runway 23. The pilot kept thinking that he was following his clearance despite some anomalies in the instructions being issued to other aircraft such as the 737. These cues elicited some concern by the Seminole pilot but the pilot did not take further action to clarify the significance of these cues. The pilot of the Seminole was instructed to track for a left hand circuit for runway 23 prior to infringing the extended runway 23 centreline. It is plausible that the pilot had regressed or been captured by his former more frequent habits (glider towing, general flying, and gliding) which required right hand circuits off runway 23 at Gawler airfield. The pilot's default mental model was right hand circuits off a runway 23 configuration. This strong habit intrusion, that is, the unintended activation of the strongest or most contextually frequent action schema most probably contributed to this occurrence.