A319 FLT CREW OVERSHOOTS ALT IN CLB; CREATING CONFLICT WITH TFC ABOVE.

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DEPARTING SNA; THE CAPT WAS FLYING AND THE AUTOPLT HAD NOT YET BEEN ENGAGED. SOCAL HAD GIVEN US CLRNC TO 13000 FT WITH A SPD RESTR OF 250 KTS UNTIL REACHING THAT ALT. WE WERE SWITCHED TO ZLA AND GIVEN FURTHER CLB CLRNC JUST AS THE ACFT BEGAN TO LEVEL OFF. I READ BACK THE NEW ALT AND DIALED IT INTO THE ALERTER AND POINTED. THE CAPT RESPONDED WHILE POINTING AT THE ALT THEN ASKED ME TO 'PULL' ON THE ALERTER KNOB IN ORDER TO SELECT THE 'OPEN CLB' MODE. WE CONTINUED THE CLB AND APCHING 16000 FT; RECEIVED A TCAS TA. I REDUCED RANGE AND NOTED AN ACFT AT 17000 FT SLIGHTLY S OF US. WE ACQUIRED IT VISUALLY AND NOTED THAT IT WAS DIVERGING TO OUR R. THE CAPT HAD STOPPED THE CLB BY 16600 FT WITH THE TFC NOW ABOUT 3.5 MI AWAY. I RPTED THE TFC TO ZLA. THEY RESPONDED THAT OUR CLRNC ALT WAS 16000 FT AND TOLD US TO 'MAINTAIN SIXTEEN THOUSAND.' I RPTED THAT WE WERE DSNDING TO MAINTAIN 16000 FT. WE THEN BOTH LOOKED AT THE ALERTER WINDOW. IT WAS SET TO 17000 FT. WE RESET IT TO SIXTEEN AND LEVELED OFF. IN DISCUSSING WHAT HAD HAPPENED; WE AGREED THAT WE HAD FOLLOWED PROPER PROC IN SETTING THE ALERTER: EACH POINTING AND THE PF RESTATING THE ALT. IT WAS INCONCEIVABLE TO US THAT I WOULD HAVE READ BACK SIXTEEN; BUT DIALED SEVENTEEN INTO THE WINDOW WITHOUT ONE OF US REALIZING THE MISTAKE. AFTER LNDG IN DENVER; THE CAPT CALLED THE CTR AND WAS INFORMED THAT THEY HAD LISTENED TO THE TAPE AND I HAD INDEED READ BACK SIXTEEN THOUSAND. THE ONLY OTHER IDEA WE COULD COME UP WITH FOR HOW THIS MAY HAVE HAPPENED IS THAT IN PULLING ON THE ALERTER KNOB TO CONTINUE OUR CLB; I MIGHT HAVE TWISTED IT AND CHANGED THE SET ALT WITHOUT EITHER OF US NOTICING. I TRIED TO DUPLICATE THIS ON THE GND; BUT DEEMED IT UNLIKELY DUE TO THE AMOUNT THE KNOB HAD TO BE TURNED TO CHANGE THE ALT.