WDB FAILED TO CLR THE RWY AS INSTRUCTED; MLG LANDED WHILE WDB ON RWY.

Narrative

WE WERE CLRED FOR A VISUAL APCH TO RWY 10L AT PIT. WE WERE FOLLOWING A WDB Y. WHEN WE CHANGED OVER TO TWR FREQ (128.3) THE TWR ADVISED US THAT WE WERE 3 MI BEHIND THE HVY; CAUTIONED US ON WAKE TURBULENCE AND CLRED US TO LAND. SHORTLY THEREAFTER THE WDB Y CREW REQUESTED PERMISSION TO 'ROLL TO THE END.' TWR ADVISED THEM THAT THERE WAS LNDG TFC 3 MI IN TRAIL AND THAT A ROLL TO THE END COULDN'T BE PERMITTED. WE WERE ONLY SEVERAL HUNDRED FT OFF THE RWY WHEN THE WDB Y ROLLED BY HIS LAST OPPORTUNITY TO CLR ON A HIGH SPD TAXIWAY (N-4). I ADVISED MY FO TO STANDBY FOR A GAR. THE TWR CTLR CAME ON AND DIRECTED THE WDB Y TO MAKE THE NEXT R TURN (N-3) AND THEN RECLRED US TO LAND. THE WDB Y ROLLED BY N-3 ABOUT THE TIME WE TOUCHED DOWN. HE FINALLY DID CLR AT THE END AND WE CLRED AT N-5. FOR SEVERAL SECONDS WE WERE BOTH ON THE ACTIVE LNDG RWY. THE WDB Y HAD AGREED TO CLR AT N-3 AND BOTH THE CTLR AND I BASED OUR MOVES ON HIS ACKNOWLEDGEMENT OF THE TAXI CLRNC. NOTHING FURTHER WAS SAID ABOUT WHAT HAPPENED AND NO TELEPHONE CALLS WERE REQUIRED BUT I AM CONCERNED ABOUT WHAT HAPPENED.