CABIN ATTENDANTS ABOARD A320 FAIL TO DISARM SLIDE PRIOR TO OPENING DOOR ON ARRIVAL. SLIDE DEPLOYS.

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AFTER LNDG AND TAXIING TO THE GATE AND THE SEATBELT SIGN TURNED OFF; I HEARD THE PURSER SAY TO DISARM DOORS FOR ARR. AS I STARTED TO LIFT THE HANDLE I SAW THE WHITE LIGHT BLINK ON. MY FIRST THOUGHT WAS THAT THE CABIN WOULDN'T STILL BE PRESSURIZED. MY SECOND THOUGHT WAS I WONDERED IF THIS DOOR WAS GOING TO CAUSE PROBS LIKE DOOR 2L. (UPON LEAVING; I ARMED BOTH DOOR 2L AND 2R AFTER THE ARM DOORS ANNOUNCEMENT WAS MADE. FLT ATTENDANT #3 WAS IN THE AISLE ATTENDING TO PAX. DOOR 2L WOULDN'T ARM. I FELT THE DOOR NEEDED TO BE OPENED AND RE-CLOSED SO I CALLED THE CAPT FOR HIS APPROVAL; WHICH HE GAVE. AFTER OPENING THEN CLOSING 2L; IT ARMED PROPERLY. I TOLD FLT ATTENDANT #3 ABOUT THIS WHEN SHE CAME TO THE AFT OF THE ACFT.) SO I PULLED THE HANDLE UP A LITTLE STRONGER AND THE DOOR OPENED (I WONDERED WHY -- THAT SHOULDN'T BE HAPPENING) AND THE SLIDE INFLATED; AT WHICH POINT I FINALLY REALIZED I PULLED UP THE WRONG HANDLE. SUPVRS CAME ON BOARD TO TAKE A LOOK. SLIDE WAS DETACHED FROM THE PLANE AND THE DOOR WAS CLOSED.