As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON LANDING WHILE ENGINES WERE IN REVERSE SMOKE APPEARED IN CABIN. ENGINE BLEEDS AND PACKS WERE SHUT OFF PROBLEM WENT AWAY. *S/D* UNKNOWN CAUSE. SEATTLE MAINTENANCE TRIED TO DUPLICATE PROBLEM BY RUNNING ALL ENGINES AND PACKS, AND CYCLEING REVERSERS. PROBLEM COULD NOT BE DUPLICATED.