B737 WITH ZDC DSNDING FROM FL270 TO FL260 SEEKING A SMOOTHER RIDE EXPERIENCED TCASII RA.

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WE WERE LEVEL AT FL270; AN INTERMEDIATE LEVELOFF ALT; AWAITING CLRNC FROM ZDC TO OUR FILED ALT OF FL310. WHEN ADVISED THAT FL310 WAS BUMPY; WE WERE TOLD TO CHOSE BTWN FL260 AND FL280. FL260 WAS SMOOTH AND THE CTLR CLRED US TO DSND TO FL260. PASSING FL267; THE TCASII ALERT OF 'TFC; TFC' SOUNDED. I ADJUSTED MY RANGE SCALE TO 10 NM AND SAW A TARGET IN YELLOW 1500 FT DIRECTLY BELOW ME AND CLBING. BY THE TIME WE HAD DETERMINED THE ACFT BELOW US WAS INDEED CLBING AND IN CONFLICT; THE TCASII SOUNDED THE 'CLB; CLB' RA AND WE RESPONDED ACCORDINGLY AND WITH GREAT DIFFICULTY; DUE TO SO MUCH RADIO TFC; ANNOUNCED OUR RESPONSE TO AN RA TO THE ZDC CTLR. THE CLOSEST I SAW ON THE TCASII DISPLAY WAS A VERT SEPARATION OF APPROX 700 FT. THE CTLR THEN TOLD US TO MAINTAIN FL270 ONCE THE CONFLICT WAS NO LONGER PRESENT AND TOLD US THAT THE AIRSPACE BELOW FL270 WAS OWNED BY ANOTHER CTLR WHO TOLD THE CTLR TO USE IT IF THE CTLR NEEDED TO AND THAT IS WHY THE CTLR CLRED US TO FL260. UPON CHANGING FREQS. THE CTLR APOLOGIZED FOR THE CONFUSION. WHEN TCASII BARELY PREVENTS A LOSS OF SEPARATION; IS A FULL CTLR INVESTIGATION INITIATED AS IF A LOSS OF SEPARATION ACTUALLY HAPPENED?