As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING POWERBACK, SMOKE ACCUMULATED IN THE CABIN AND THE FORWARD LAVATORY SMOKE DETECTOR ACTIVATED. AIRCRAFT RETURNED TO THE GATE AND THE PASSENGERS WERE UNLOADED. INSPECTED AND OPERATIONALLY CHECKED THE AIRCRAFT SYSTEMS. COULD NOT DUPLICATE THE PROBLEM. OPERATIONAL CHECK GOOD.