A WDB ACR ACFT OVERSHOT ITS ALT ON DSCNT WHILE TRYING TO SOLVE A MECHANICAL PROB PRIOR TO DUMPING FUEL.

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DURING CLBOUT FROM HNL ENRTE TO NRT WE EXPERIENCED MECHANICAL PROBS WITH 1 LEADING EDGE FLAP. DURING OUR TROUBLESHOOTING AND ASSESSMENT OF THE SIT; ATC INSTRUCTED US TO DSND TO 15000 FT. WHILE DEEPLY INVOLVED WITH THE FLT MANUAL IRREGULAR PROC AND WITH COMPANY COMS; I FELT THE ACFT G-LOADING INCREASING ABNORMALLY. I LOOKED UP AND SAW US IN A CLBING TURN AND ALT OF ABOUT 14600 FT. I CHKED THE ALT SELECT WINDOW; SAW 15000 FT; AND ASSUMED THAT THE PF HAD INADVERTENTLY DSNDED THROUGH THE ASSIGNED ALT AND WAS CORRECTING AGGRESSIVELY. WE LEVELED OFF AT 15000 FT AND CONTINUED OUR IRREGULAR OP. AT THE TIME OF THE INCIDENT; THE COCKPIT WAS EXTREMELY BUSY AND NOISY; PARTIALLY DUE TO THE DISTR CAUSED BY A FLT ATTENDANT IN THE COCKPIT RPTING ON HIS PERCEPTION OF RELEVANT SIGHTS/SOUNDS ASSOCIATED WITH THE MECHANICAL PROB. ALSO; THE CAPT WAS THE PF AND WAS TASK-SATURATED WHILE TRYING TO LISTEN TO ALL INPUTS FROM ALL SOURCES. I DO NOT KNOW WHY THE FO DID NOT CATCH THE ALTDEV; BUT I SUSPECT IT WAS BECAUSE HE TOO WAS DISTRACTED BY ALL THE COCKPIT ACTIVITY. PERHAPS BETTER DIVISION OF COCKPIT DUTIES (E.G.; HAVING THE FO FLY THE ACFT WHILE THE CAPT MANAGED THE OVERALL SIT) WOULD HAVE LESSENED THE CHANCES OF SUCH AN INCIDENT. SUPPLEMENTAL INFO FROM ACN 229826: WE WERE RETURNING TO HNL BECAUSE OF A LEADING EDGE DEVICE MALFUNCTION. CTR CLRED US TO MAINTAIN 15000 FT PRIOR TO FUEL DUMP. LIGHT TO MODERATE TURB; RAIN AND SPD RESTRICTIONS DUE TO SLAT MALFUNCTION; AS WELL AS PREPARING FOR FUEL DUMP.