FLC OF ACR MLG ACFT DEVIATED FROM ASSIGNED ALT WHEN RESPONDING TO A TCASII RA.

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CRUISING AT 14000 FT; ZDC (133.9) ADVISED VFR TFC (SMT ACFT) CLBING THROUGH OUR ALT AT 1030 O'CLOCK POS 7 MI AND HE HAD US IN SIGHT -- WE ADVISED WE DIDN'T HAVE TFC IN SIGHT. TFC WAS MOVING TO OUR 9 O'CLOCK POS AND CLOSING AND STILL NOT IN SIGHT. AN RA CAME ON INDICATING THE TARGET WAS 400 FT BELOW US AND CLBING -- TCASII RECOMMENDED 1800 FT DSCNT -- AUTOPLT WAS DISCONNECTED AND DSCNT WAS INITIATED MANUALLY. THE RA CLRED AT 13300 FT AND WE CLBED BACK UP TO 14000 FT. THE TFC SEPARATION THAT THE CTLR GAVE THE SMT ACFT (HE WAS WORKING HIM VFR) WAS NOT A CONCERN TO HIM BECAUSE THE CTLR SAID THE SMT ACFT HAD US IN SIGHT. OUR TCASII ENVELOPE WAS PENETRATED BY THIS ACFT AND WITHOUT US HAVING VISUAL CONTACT; WE RESPONDED PER PROC. I BELIEVE SINCE THE SMT ACFT SAID HE HAD US VISUALLY; HE SHOULD HAVE ALTERED HIS COURSE; FOR MORE AND SAFER SEPARATION FOR BOTH OF US! AFTER ADVISING THE CTLR OF OUR EVASIVE ACTION; DUE TO TCASII PROCS; HE WAS COMPLETELY UNAWARE OF OUR REQUIREMENT TO HAVE TO RESPOND TO THE DIRECTIONS OF THE TCASII IN THIS SITUATION.