B767 PF ACKNOWLEDGES A CLB CLRNC MEANT FOR ANOTHER ACFT; IS CHALLENGED BY ZID; AND RETURNS TO INTENDED ALT PRIOR TO LOSS OF SEPARATION.

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FLT XXX; A B767-300; DEPARTED CVG AT XA00Z ENRTE TO SLC; WITH A PLANNED CRUISING ALT OF FL350. THE FLT WAS INSTRUCTED TO CLB AND MAINTAIN FL310. THE FLC ACKNOWLEDGED THE CLRNC AND DIALED 31000 FT IN THE MCP ALT WINDOW. THE FLT LEVELED OFF AT FL310; AND THE PNF ADVISED THE PF TO MONITOR VHF #1; THE PRIMARY ATC RADIO; AS THE PNF WAS GOING TO MAKE A PA ANNOUNCEMENT. AFTER THE PA WAS COMPLETED; THE PF BRIEFED THE PNF AT XA15Z THAT HE HAD RECEIVED AND ACKNOWLEDGED A CLRNC TO FL330. THE ALT INDICATOR ON THE MCP INDICATED 33000 FT; AND A CLB HAD BEEN COMMENCED TO FL330. LEAVING FL325; THE ATC CTLR ASKED FLT XXX; 'WHAT IS YOUR ALT?' THE PNF REPLIED; 'LEVELING AT FL330.' THE CTLR ADVISED THAT FLT XXX WAS ONLY CLRED TO FL310; AND INSTRUCTED FLT XXX TO DSND IMMEDIATELY TO FL310; AND 'EXPEDITE' AS CONFLICTING TFC AT FL330 WAS 2 O'CLOCK POS AND 18 MI. FLT DSNDED TO FL310 AND WAS LEVEL AT FL310 WHEN THE CONFLICTING TFC WAS RPTED AT 10 NM. THE PNF DID NOT ACKNOWLEDGE THE CLRNC TO CHANGE ALT BECAUSE HE WAS ATTENDING TO OTHER COMPANY RELATED DUTIES.