FLIGHT CREW IS INSTRUCTED TO LINE UP AND WAIT AFTER LANDING AIRCRAFT ON FINAL. AS CREW BEGINS TAXI THEY NOTICE ANOTHER AIRCRAFT DOING THE SAME; ONE TAXIWAY WEST. TOWER HAD GIVEN TWO AIRCRAFT THE SAME CLEARANCE.

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WE WERE INSTRUCTED TO TAXI TO THE RWY 26R HOLDING POINT AT A14; AND INFORM THE TWR WHEN READY. WE CALLED THE TWR AND WERE INSTRUCTED TO LINE UP AND WAIT AFTER THE ARRIVING A340 ON FINAL. I WAS COMMUNICATING WITH ATC AND ACKNOWLEDGED THE CLRNC. THE A340 WAS ON A LONG FINAL AND THE CAPT ELECTED TO STOP AT THE CAT2 HOLD LINE INSTEAD OF THE CAT1 LINE. I WAS AWARE OF THIS BUT DID NOT SAY ANYTHING; BECAUSE I DIDN'T THINK IT WAS WORTH OPENING UP A CAN OF WORMS REGARDING WHERE TO STOP THE AIRPLANE; IN A CRITICAL POINT IN THE TKOF ENVIRONMENT; AND WANTED TO CONCENTRATE ON WHAT WAS GOING ON NEAR THE RWY AND NOT PRODUCING UNNECESSARY DISCUSSION ON WHERE TO STOP THE AIRPLANE. AFTER ALL WE HAD NOT ENCROACHED ON THE RWY AND COULD ALWAYS MOVE UP IF SO REQUESTED. THE TWR THEN ASKED US TO MOVE UP TO THE RWY HOLD SHORT LINE; BUT WE DID NOT HEAR ANY REQUEST TO HOLD SHORT. IT SEEMED REASONABLE TO US THAT THE TWR SIMPLY WANTED US UP TO THE HOLD SHORT LINE SO AS TO EXPEDITE OUR TAXIING ON TO THE RWY AFTER THE LNDG TFC. I TOLD THE TWR WE WERE MOVING UP; BUT NEVER ACKNOWLEDGED ANY HOLD SHORT REQUEST; WHICH THE TWR DID NOT QUESTION. EVIDENTLY THE TWR WANTED US TO MOVE UP TO THE HOLD SHORT LINE TO GET ANOTHER ACFT OUT FROM ANOTHER INTXN OFF TO OUR R. WHEN THE A340 LANDED WE BEGAN TO TAXI INTO POS WHEN WE SAW THE OTHER AIRPLANE OFF TO OUR R DO THE SAME. THE CAPT STOPPED AND THE OTHER PLANE TOOK THE RWY; HOWEVER WE HAD CROSSED THE HOLD SHORT LINE. WE WERE THEN CLRED FOR TKOF; WITHOUT INCIDENT. THE TWR THEN APOLOGIZED FOR THE CONFUSION WHEN WE WERE HANDED OFF TO DEP. OUR CLRNC TO INITIALLY POS AND HOLD WAS NEVER CANCELED; NOR WERE WE EVER INSTRUCTED TO HOLD SHORT OF THE RWY; AND IF WE WERE THE TWR NEVER QUESTIONED OR ASKED US TO CONFIRM A HOLD SHORT REQUEST.