ACR CAPT DESCRIBED CONFUSING ATC CLRNC DURING LNDG ROLL REF TURN OFF POINT; CITING TIMING OF CTLR'S CLRNC AS CONTRIBUTORY.

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THE FO PERFORMED A NORMAL LNDG ON RWY 12 AT MIA. SLOWING FOR EXIT OFF THE RWY; ABOUT 80 KTS; TWR TOLD US TO CONTINUE OUR ROLLOUT; AND I THOUGHT I HEARD HIM SAY 'TO THE END.' THE FO TOLD ME LATER THAT HE HEARD INSTRUCTIONS TO EXIT AT TXWY S. APCHING 70 KTS; I ROGERED THE INSTRUCTIONS AND REPEATED; 'ROLL TO THE END.' AT THE SAME TIME I CALLED 70 KTS AND RECEIVED CTL OF THE ACFT. TWR WAS HANDLING AT LEAST 2 RWYS WITH ALMOST NON-STOP XMISSIONS. PASSING TXWYS S AND T; I SAW AN ACFT EXITING OUR RAMP AND WAS THINKING THAT WAS WHY WE WERE ROLLING SO FAR DOWN THE RWY. 2 SECONDS LATER THE TWR ASKED ME IN AN EXCITED MANNER IF WE COULD HOLD SHORT ON RWY 12. WE WERE APCHING THE LAHSO MARKINGS FOR RWY 9. REACTING TO THE CTLR'S TONE OF VOICE; I BRAKED HARD AND STOPPED AT THE LAHSO MARKINGS. WE DID NOT HAVE TIME TO RESPOND ON THE RADIO PRIOR TO STOPPING. THE CTLR THEN TOLD US TO ACCELERATE THROUGH RWY 9. FROM A FULL STOP IT TOOK AT LEAST 15 SECONDS FOR THE ENGS TO SPOOL BACK UP AND FOR US TO BEGIN MOVING. THE FO WAS LOOKING OUT HIS SIDE WINDOW AND SAW AN ACFT ABOUT 500 FT ON FINAL TO RWY 9. HE SAID THAT I SHOULD HURRY AND WE CROSSED PRIOR TO THE OTHER ACFT TOUCHING DOWN. THIS EVENT WAS EXCITING; BUT COULD HAVE BEEN A LOT WORSE. TWRS FREQUENTLY GIVE INSTRUCTIONS TO ACFT AS THEY ARE SLOWING AND GETTING READY TO EXIT. FREQUENTLY THE 2 ACTIONS CAUSE INTERFERENCE AND SOMETIMES CONFUSION. SINCE THE ARPT WAS NOT UTILIZING LAHSO THEY PROVIDED ADEQUATE SEPARATION. IF WE HAD BEEN ALLOWED TO CONTINUE SLOWING AND EXIT PRIOR TO TXWY S THIS WOULD HAVE BEEN AVOIDED. THE DIFFERENCES BTWN WHAT WE HEARD DEMONSTRATES THAT THIS IS A BAD TIME TO TALK TO US.