GLF3 TAXIES ONTO RWY 25R AT MKE WHILE A BE18 IS ON IT'S TKOF ROLL AND MUST VEER AROUND THE ACFT.

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ACFT X; A GLF3 WAS TAXIING FOR DEP. ACFT Y A BE18; WAS ON TKOF ROLL FROM RWY 25R AS ACFT X ROLLED ONTO RWY 25R. THIS OCCURRED AT THE INTERSECTION OF RWY 25R AND TXWY E; ABOUT 1500 FROM THE APCH END. ACFT Y WAS ISSUED A 'CANCEL TKOF CLRNC' BUT DECIDED TO CONTINUE -- PROBABLY DUE TO THE CLOSE PROXIMITY OF ACFT X. ACFT Y WAS ABLE TO VEER L AND PASS; BY MY ESTIMATION ABOUT 10 FT OFF THE NOSE OF THE GLF3 -- WHO; EVEN AFTER BEING TOLD TO 'STOP!' RATHER EMPHATICALLY BY GND CTL; WAS STILL MOVING UNTIL THE BE18 WHIZZED PAST HIM. ACFT X HAD BEEN ISSUED EXPLICIT TAXI INSTRUCTIONS; INCLUDING A 'HOLD SHORT OF RWY 25R' WHICH HE READBACK. HE THEN REQUESTED CLARIFICATION ON THE ROUTE. MY PERSPECTIVE? GND CTL PROBABLY SHOULD'VE REITERATED THE HOLD SHORT INSTRUCTION WITH THE ROUTE CLARIFICATION; THOUGH IT ISN'T REQUIRED. ACFT X SHOULD NOT HAVE KEPT MOVING WITHOUT KNOWING WHERE HE WAS -- ESPECIALLY KNOWING HE HAD TO HOLD SHORT SOMEWHERE. IT SHOULD BE NOTED ALSO; THAT ACFT X WAS ENGAGED IN A CHECK RIDE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR INDICATED THAT THE GLF3 DID NOT STOP TAXIING UNTIL THE BE18 PASSED DIRECTLY IN FRONT OF THEM.