What was found
GROUND CREW OBSERVED BURNING FUEL IN APU EXHAUST AFTER POST FLIGHT SHUTDOWN. REPORTED TO ATC, LOCAL CFR DISPATCHED. CAPTAIN RE-STARTED APU THEN PERFORMED APU SHUTDOWN WITHOUT FURTHER INCIDENT. APU DIFFERED ON 08/11/11, REF TL -213273-2011, DEF-049091-2011 THEN REPLACED, REF TL-213279-2011.