MD80S ACFT IN CRUISE WAS GIVEN DSCNT CLRNC. JUST AS CLRNC RECEIVED FLT ATTENDANT RPTED FUMES IN THE ACFT. FO WENT BACK TO CHK BEFORE SETTING IN THE NEW ALT; BUT CAPT RPTR SETS IT IN ERROR. CTLR INTERVENES WHEN NOTING ACFT DSNDING THROUGH ASSIGNED.

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CRUISING AT FL350 WORKING ZOB. RECEIVING CLRNC FROM CLE WHEN FLT ATTENDANT CAME THROUGH DOOR RPTING FUMES IN FORWARD GALLEY. FO READ BACK CLRNC AND BOTH HE AND I ASKED FLT ATTENDANT SEVERAL BRIEF QUESTIONS. I WAS FLYING AND ASKED FO TO GO BACK AND INVESTIGATE. I THEN NOTICED THAT OUR NEW DSCNT ALT HAD NOT BEEN SET AND I DID SO AS THE FO WAS LEAVING THE COCKPIT. I SET FL290 HAVING UNDERSTOOD OUR CLRNC AS DSND AND CROSS DEWIT INTXN AT FL290 AND 290 KTS. APPROX LEAVING FL310 DSNDING CLE ISSUED A SPD REDUCTION TO 280 KTS. ABOUT 30 SECONDS LATER I ASKED IF THEY WANTED THE SPD OR ALT AT DEWIT. THEY ASKED OUR ALT; WHICH I AM NOT CERTAIN OF AT THIS TIME; BUT I KNOW IT WAS WELL ABOVE FL290 BUT CLOSE TO; IF NOT BELOW; FL310. CLE CLRED TO FL280 AND COMMENTED THAT OUR ORIGINAL ASSIGNED ALT HAD BEEN FL310 NOT FL290. FO RETURNED TO THE COCKPIT A FEW MINS LATER AND I EXPLAINED TO HIM WHAT HAD OCCURRED. OBVIOUS CASE OF DISTR; COUPLED WITH POOR COCKPIT DISCIPLINE TOWARDS ALT SETTING AND VERIFICATION PROCS; BY BOTH MYSELF AND FO.