TCASII LOGIC ACR X SAME ALT ASSIGNED TCASII RA CLB HAD LTSS FROM ACR Y. SYS ERROR.

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ACR X; AT FL295 WHILE DSNDING FROM FL330 TO FL290 ASSIGNED; AT 290 KIAS APPROX 56 SW MOL (MONTEBELLO VOR) WE EXPERIENCED A TCASII RA EVENT. WE WERE WORKING ZDC ON 133.02 ON AN APPROVED WX DEV BTWN CUMULO NIMBUS BUILDUPS WITH GOOD INFLT VISIBILITY WHEN WE OBSERVED A YELLOW TFC SYMBOL ON TCASII DISPLAY AT APPROX 1 O'CLOCK POS; 6 MI; PLUS 100 FT ABOVE OUR ALT. ZDC THEN CALLED THAT ACR Y TO US AND ORDERED AN IMMEDIATE DSCNT TO FL250. PF (CAPT) DISCONNECTED THE AUTOPLT AND INITIATED AN IMMEDIATE DSCNT WHILE FO VISUALLY SEARCHED FOR THE TFC. WE RECEIVED A TCASII RA TO 'CLB; XING CLB' (WITH A COMMANDED PLUS 2500 FPM CLB) WHEN ALREADY ESTABLISHED IN THE DSCNT SO WE CONTINUED TO DSND. THE DSCNT RATE BECAME APPROX 4000 FPM. THE ALT DIFFERENCE OF THE TFC INDICATED ON THE TCASII DISPLAY WENT FROM PLUS 100 FT TO PLUS 900 FT DURING THE MANEUVER AND NEVER SHOWED LEVEL WITH US. THE TFC PAST DIRECTLY IN FRONT OF US AND THEN CONTINUED OVER TO OUR 9 O'CLOCK POS AT ABOUT 2 MI; PLUS 900 FT ON TCASII DISPLAY. WE NEVER VISUALLY SPOTTED THE TFC WHEN THE 'CLR OF CONFLICT' WAS ANNOUNCED BY TCASII. THE ENTIRE EVENT LASTED APPROX 30 SECONDS; THEN WE SHALLOWED THE DSCNT RATE AND LEVELED AT FL250 ASSIGNED. I COMMENTED TO CTR THAT IT WAS CLOSE; AND THEY REPLIED 'YES IT WAS.' THE SECTOR CTLR WAS APPARENTLY WORKING NUMEROUS WX DEVS AT THE TIME; AND SOUNDED VERY BUSY. WE DID NOT HEAR CTR IDENT OR ISSUE ANY INSTRUCTIONS TO THE OTHER ACFT; SO WE DO NOT KNOW WHAT THE TFC WAS OR IF CTR RECORDED A 'LOSS OF SEPARATION' EVENT. THE PAX HAD ALREADY BEEN SEATED PRIOR TO THE MANEUVER AND THE FLT ATTENDANTS RPTED NO PROBS. WE FINISHED OUR WX DEV; SWITCHED FREQS; AND CONTINUED ON TO OUR DEST WITH NO FURTHER PROBS.