ZID EXCHANGES TFC BTWN E145 AND OTHER IFR ENRTE ACFT. CTLR ISSUES ALT CHANGE TO E145 THAT CONFLICTS WITH ENRTE TFC. CTLR OBSERVES CONFLICT; ATTEMPTS TO CORRECT CONFLICT; BUT APPEARS UNABLE TO MAINTAIN LEGAL SEPARATION.

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WE (X) HAD BEEN CLRED TO 17000 FT. AS WE CLBED THROUGH 16000 FT; THE CTLR CALLED 'TFC AT 1 O'CLOCK POS; 8 MI; SBOUND; WILL BE 1000 FT ABOVE YOUR ALT; MAINTAIN FL180.' WE ACKNOWLEDGED LOOKING FOR THE TFC; MAINTAIN FL180. HE THEN ISSUED US AS TFC TO THE OTHER ACFT (Y) AND TOLD THEM WE WOULD BE 1000 FT BELOW THEIR ALT. AS WE CLBED THROUGH 17300 FT THE CTLR TOLD US TO MAINTAIN 17000 FT; THAT OUR TFC WAS AT 18000 FT. I IMMEDIATELY DISENGAGED THE AUTOPLT AND BEGAN A DSCNT; BUT WE REACHED 17500 FT BEFORE STARTING BACK DOWN. AT THIS POINT THE TFC WAS WITHIN 5 MI; HOWEVER THEY PASSED BEHIND US AFTER WE WERE LEVEL AT 17000 FT. OUR TCASII NEVER ISSUED AN RA; HOWEVER IT DID GIVE US A HEADS UP ON THE TFC. WE WERE GOING TO VERIFY THE CLRNC WHEN CTR CALLED. IN ISSUING THE TFC; CTR DID NOT GIVE OUR ALTS; JUST '1000 FT ABOVE AND 1000 FT BELOW.' CTR LATER ASKED IF WE HAD EXCEEDED 17000 FT AS THEY HAD A DISCREPANCY WITH OUR ALT. IT LOOKED TO US LIKE A CTLR ERROR; HOWEVER IF A CLRNC IS NOT CLR IN THE FUTURE; I'LL VERIFY IT IMMEDIATELY.