GND CTLR APPEARS TO HAVE BEEN CONCERNED ABOUT TFC SPACING AND CHANGED THE CLRNC. HOWEVER; THE RPTR'S ACFT WAS ALREADY ON THE RWY. NO RWY INCURSION OCCURRED; AND THERE WAS NO LOSS OF SEPARATION.

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TAXIING OUT OF OUR RAMP AT INTXN OF TXWY C AND TXWY B1. GND CTL CLRED US TO TAXI TO RWY 18R. I ACKNOWLEDGED TAXI RWY 18R. CAPT HEARD SAME. CAPT AND I BOTH SAW AM ACFT ON FINAL (APPROX 4 MI OUT) FOR RWY 18L. WE BOTH WERE SURE NO IMMINENT DANGER OR CONFLICT EXISTED; WE BEGAN TO CROSS RWY 18L. THE ACFT NOSE WAS 1/2 WAY ACROSS RWY 18L WHEN GND CALLED AND ASKED US TO HOLD SHORT RWY 18L. I IMMEDIATELY RESPONDED 'NEGATIVE; UNABLE; WE WERE CLRED TO RWY 18R.' CAPT SIMULTANEOUSLY STATED 'CAN'T DO IT.' NEXT; GND CTLR SAID 'TAXI ACROSS RWY 18L WITHOUT DELAY; MONITOR TWR 124.3' THIS IS A CASE; I BELIEVE; OF 1 OF 2 THINGS. 1) THE CTLR GOT RWY 18L AND RWY 18R MIXED UP IN THE ORIGINAL CLRNC; OR 2) THE CTLR SENT US TO RWY 18R ON PURPOSE ORIGINALLY; CONSIDERING CLRNC WITH LNDG TFC SUFFICIENT; THEN CHANGED THEIR MINDS AT A POINT IT WAS TOO LATE FOR US TO STOP. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR BELIEVES THAT GND CTLR WAS HAVING DIFFICULTY JUDGING TFC SPACING AND THUS CHANGED THE CLRNC. NONETHELESS; NO RWY INCURSION OCCURRED; AND WITH 4+ MI BTWN LNDG AND XING TFC; NO TFC CONFLICT OCCURRED.