AN A300'S #1 THRUST REVERSER WAS MEL'ED AND LOCKED OUT PRIOR TO FLIGHT. AFTER TAKEOFF THE GREEN #1 REVERSER DEPLOYED LIGHT AND ASSOCIATED ECAM ILLUMINATED. AN EMERGENCY WAS DECLARED WITH A RETURN TO LAND.

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THIS WAS A RESERVE ASSIGNMENT. CALLED OUT OF ORDER ON FIRST DAY TO FLY FLIGHT TO ZZZ1 DUE TO THE NEED TO HAVE A LINE CHECK. GOT TO AIRCRAFT AND MAINTENANCE WAS DEFERRING THE #1 THRUST REVERSER DUE TO A DEPLOYMENT LIGHT ON THE LAST FLIGHT. PAPERWORK COMPLETED; WITH #1 THRUST REVERSER DEFERRED; AND AIRCRAFT DOWNGRADED TO CAT IIIA. EVERYTHING CHECKS GOOD PAPERWORK WISE. I WAS THE PILOT FLYING. ALL NORMAL OPERATIONS UNTIL PASSING 11000 FT ON CLIMBOUT. WE THEN GOT THE GREEN #1 'REVERSER DEPLOYED' LIGHT; WITH THE ASSOCIATED ECAM AND WARNINGS. CRITICAL ACTION ITEMS COMPLETED (THRUST REVERSER DEPLOYED INFLIGHT) FOLLOWED BY RUNNING THE ECAM. WE LEVELED OFF AT 12000 FT; SLOWED TO 250 KTS; AND GOT VECTORS TO STAY IN THE LOCAL AREA. I FLEW AND HANDLED THE #1 RADIO. FIRST OFFICER HANDLED ALL OTHER COORDINATION WITH FIRST ATC; THE DISPATCH; THEN MAINTENANCE. CHECK AIRMAN BACKED US UP. EMERGENCY WAS DECLARED AND WE COORDINATED TO RETURN TO ZZZ. THE 'REVERSER' LIGHT AND ECAM WARNINGS WERE INTERMITTENT AND KEPT THE CRC GOING; SO THE EMERGENCY CANCEL SWITCH WAS USED TO SILENCE THE BELL. #1 THRUST LEVER WAS LEFT AT IDLE FOR THE REMAINDER OF THE FLIGHT. ALL CHECKLISTS WERE RUN. CHECK AIRMAN WAS KEPT INTO THE LOOP TO USE HIS EXPERIENCE TO MAKE SURE WE DIDN'T OVERLOOK ANYTHING. WEATHER WAS 800 FT OVERCAST AND 1 1/2 MILES WITH RAIN; WINDS 340 DEGREES AT 16 KTS. VECTORS BACK TO ILS RUNWAY 35L WITH NORMAL APPROACH AND LANDING. FIRE CREW FOLLOWED US TO RAMP. DEBRIEFED MAINTENANCE AT THE AIRPLANE. IT SEEMS THAT MAINTENANCE WAS A LITTLE MORE UNDER THE IMPRESSION THAT WE SHOULD HAVE KEPT GOING SINCE THE REVERSER WAS DEACTIVATED. THAT'S FINE; BUT THEN THE 'REVERSER' LIGHT AND THE ECAM SHOULD NOT HAVE COME ON EITHER. YOU CAN'T HAVE IT BOTH WAYS. I TOLD HIM THAT CONTINUING WOULD HAVE BEEN HARD TO JUSTIFY TO THE FAA. THIS ISSUE SOUNDS LIKE IT NEED TO BE TALKED ABOUT AT A HIGHER LEVEL; SINCE IT WOULD INVOLVE MELS; CHECKLISTS; AND A PHILOSOPHY CHANGE TO CONTINUE WITH THE ECAMS AND CRC GOING OFF INTERMITTENTLY.