A B777 FLT CREW TAXIED IN TO THE GATE AND POSITIONED THE FUEL CUTOFF LEVERS TO OFF BUT NOTICED A FEW MOMENTS LATER ONE ENGINE WAS STILL RUNNING.

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PARKED AT GATE; APU RUNNING CALLED FOR BOTH ENGS TO BE SHUT DOWN. FO PLACED BOTH FUEL CUTOFF VALVES TO OFF; WE BOTH PERFORMED OUR FLOWS; AND PROCEEDED TO RUN THE PARKING CHKLIST. FO FLOW INCLUDED TURNING OFF THE ROTATING BEACON. CHKLIST ITEM 'FUEL FLOW; ZERO' REVEALED THAT L ENG WAS STILL RUNNING AT IDLE PWR. I IMMEDIATELY PLACED THE ROTATING BEACON BACK TO 'ON;' AND WE SAW A 'STATUS' MESSAGE ON THE UPPER EICAS SCREEN. STATUS PAGE REVEALED 'L ENG FUEL S/O VALVE;' INDICATING THE L ENG VALVE WAS NOT IN THE COMMANDED POS. WE WAITED APPROX 30 SECONDS MORE; NOTIFYING RAMP AND PREPARING TO USE THE FIRE HANDLE IF NECESSARY. HOWEVER; THE FUEL IN THE LINE FROM THE SPAR VALVE TO THE ENG WAS DEPLETED; AND THE ENG SHUT ITSELF DOWN. SAFETY CONCERN HERE IS THAT WE SHOULD CONSIDER A WARNING IN THE PARKING/SHUTDOWN SECTION OF THE NORMALS TO NOT TURN OFF THE BEACON UNTIL THE FUEL FLOWS HAVE BEEN CONFIRMED AT ZERO. HAD IT BEEN THE R ENG THAT CONTINUED TO RUN; WE MIGHT HAVE CAUSED DEATH OR SERIOUS INJURY BECAUSE THE GND PERSONNEL WERE DIRECTLY IN FRONT OF THE ENG OPENING CARGO DOORS AND POSITIONING CARGO HANDLING EQUIP. IN THAT GND PERSONNEL USE THE ROTATING BEACON AS AN INDICATOR OF ENGS TURNING; THE ABSENCE OF THE BEACON EVEN FOR A FEW SECONDS WHILE AN ENG CONTINUES TO RUN WITH AN ENG FUEL S/O VALVE OR VALVE MOTOR FAILURE; COUPLED WITH A MOMENT'S INATTN BY THE GND PERSONNEL; COULD RESULT IN INGESTING PERSONNEL INTO THE OPERATING ENG.