FLT CREW OF B737 RPTS UN-COMMANDED LEADING EDGE DEVICE EXTENSION AT FL400.

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REACHING CRUISE AT FL400; WE EXPERIENCED AN UN-COMMANDED LEADING EDGE DEVICE EXTENSION AT 244 KTS. THE ACFT BUFFETED AS THOUGH IT WAS IN HIGH SPEED BUFFET EVEN THOUGH IT WAS 10 BELOW BARBER POLE. I NOTICED THAT THE LE FLAPS TRANSIT LIGHT WAS ILLUMINATED [AND]; LOOKED UP AT THE LEADING EDGE DEVICE ANNUNCIATOR TO SEE ALL LEADING EDGE DEVICE IN TRANSIT. I CALLED 'FLAPS' THE CAPT CONFIRMED THAT THE FLAP HANDLE WAS IN THE 0/FLAP UP POSITION; AS HE DID SO THE LEADING EDGE DEVICE RETRACTED. WE DSNDED TO A LOWER ALTITUDE ADVISED ATC OF THAT OUR MAX SPEED WAS 240 KTS AND CONTINUED TO DEST.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: ALMOST 30 MINUTES ELAPSED FROM THE TIME THE FLAPS WERE RETRACTED AFTER TKOF AND THE UN-COMMANDED EXTENSION AT FL400. THE FLAP HANDLE APPEARED UP AND DID NOT SEEM TO MOVE WHEN PRESSURE WAS APPLIED BY THE CAPT BUT THE LEADING EDGE DEVICE RETRACTED. FOQA DATA INDICATES THAT THE LEADING EDGE DEVICE EXTENSION WAS COMMANDED AND OCCURRED AT 230 KTS. NO MAINT ACTION WAS PERFORMED TO DETERMINE IF A FAULT MAY EXIST WITH THE FLAP HANDLE OR FLAP EXTENSION SYSTEM.