A B737-300 FLT CREW INADVERTENTLY EXTENDED THE WING FLAPS AT 27000 FT IN PART BECAUSE THE FLAP HANDLE WAS NOT ENGAGED IN THE DETENT.

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I WAS THE CAPT/PF ON A NIGHT PAX FLT TO SMF WHICH WAS OUR FIRST FLT TOGETHER AS A CREW. IT WAS THE FO'S SECOND FLT ON THIS ACFT. CLBING; PASSING FL260 AND FL269; THE AUTOPLT BEGAN TO LEVEL THE ACFT AND THE FEEL OF SOME TYPE OF DRAG WAS NOTICED. I DISCONNECTED THE AUTOPLT AND NOTICED THE FLAPS WERE STARTING TO COME DOWN. I PUSHED THE FLAP LEVER TO 0 AND NOTED THE ACFT PARAMETERS. THE LEADING EDGE FLAPS LIGHT WAS AMBER BUT NEVER TURNED GREEN. THE TRAILING EDGE FLAPS WERE BTWN 0 AND 1. AFTER THE INCIDENT; I REALIZED THAT I HAD REACHED UP TO THE R CDU ABOUT 5-15 SECONDS PRIOR TO THE FLAPS COMING DOWN. IT WAS MY HABIT TO MOVE MY R-HAND AROUND THE R SIDE OF THE THROTTLES TO MAKE A CDU INPUT WHEN THE THROTTLES WERE FORWARD. I COULD HAVE MISTAKENLY BRUSHED THE FLAP HANDLE WHEN I PULLED MY HAND BACK FROM THE CDU. THE FO STATED THAT HE USUALLY CHKED THE FLAPS IN THE 0 DETENT AFTER RAISING THE FLAPS. HE COULD NOT SPECIFICALLY REMEMBER IN THIS CASE. UPON LNDG; WE REALIZED THAT THE FLAP HANDLE WOULD NOT EASILY GO TO THE 0 POS. IT THEN HAD TO BE HIT DOWN INTO THE DETENT. A LOGBOOK WRITE-UP WAS MADE. THE MECH AGREED THAT THE FLAP HANDLE WAS DIFFICULT TO MOVE FORWARD TO THE 0 POS. WE BELIEVE THAT THE FLAP OVERSPD WAS CAUSED BY 1) PNF NOT CHKING THE FLAP HANDLE IN THE 0 DETENT. 2) PF BRUSHING THE HANDLE AS HE PULLED HIS HAND BACK FROM THE R CDU. 3) POSSIBLE MIS-RIGGING OF THE FLAP HANDLE PREVENTING ITS SEATING IN THE 0 DETENT.