ZOB CTLR EXPERIENCED OPERROR OVER BUF VOR AT 17000 FT WHEN ONE ACR FLT WAS CLRED TO DSND THROUGH THE ALT OF ANOTHER ACR FLT.

Narrative

I WAS WORKING THE ROC SECTOR 31 AT THE TIME OF THE INCIDENT. PREVIOUSLY; THE BUF SECTOR BACKUP SYS FAILED; AND ALTHOUGH THERE WERE NO PROBS WITH THE RUNNING OF THE BUF SECTOR; THE TECHNICIANS WANTED TO TAKE BUF SECTOR DOWN FOR AN HR; ROUGHLY; TO ATTEMPT TO FIX IT. THIS RESULTED IN 2 POTENTIALLY BUSY SECTORS BEING MERGED INTO 1 LARGE; BUSY SECTOR. THESE SECTORS ARE NEVER COMBINED AT THAT TIME OF DAY DURING NORMAL; WKDAY TFC. I WAS FLASHED A HDOF ON ACFT X LNDG ROC. I WAS SO BUSY AT THE TIME THAT THE OTHER CTLR HAD TO CALL ME ON OUR BOUNDARY ABOUT THE HDOF. THE DATA BLOCK INDICATED ACFT X WAS DSNDING TO 11000 FT; BUT THE ACFT CHKED ON LEVEL AT FL190. I MISSED THAT; HOWEVER; AND ISSUED AN ALTIMETER; THINKING HE WAS DSNDING TO 11000 FT CROSS BUF AT 11000 FT; THE STANDARD RESTR. THUS; IN MY MIND; HE WAS SEPARATED FROM ACFT Y -- A TORONTO LANDER -- DSNDING OVER BUF TO 17000 FT. BUF WAS THE CONFLICTION POINT. WHEN I NOTICED ACFT X WAS STILL AT FL190; I TOLD HIM TO START DOWN TO 11000 FT AND HURRY. HOWEVER; BY THIS TIME; ACFT Y HAD LEVELED AT 17000 FT; AND THERE WAS NOT ENOUGH TIME FOR EVEN A FAST DSCNT BY ACFT X TO CLR UP THE SIT. I DID NOT SEE THE IMPENDING LOSS OF SEPARATION UNTIL THE CONFLICT ALERT ACTIVATED AS ACFT X SHOWED LEAVING 17900 FT. I TRIED TO SEE IF ACFT X COULD GO BACK TO FL180 BUT HE WAS ALREADY LEAVING 17400 FT AND LOOKING FOR TFC. I TURNED BOTH ACFT 30 DEGS L; NOT TO KEEP SEPARATION WHICH HAD ALREADY BEEN LOST; BUT TO KEEP THE TARGETS FROM MERGING. NEITHER PLT MENTIONED TCASII. SUPPLEMENTAL INFO FROM ACN 620092: ACFT #1 WAS DSNDING TO FL190. DATA BLOCK UPDATED TO 11000 FT. HDOF WAS INITIATED AS ACFT #2 WAS NEARING ADJACENT BOUNDARY; BUT 11000 FT WAS NOT ISSUED. MULTIPLE ACFT ON MY FREQ. ACFT #1 WAS APCHING THE ADJACENT SECTOR BOUNDARY AND SHOWING HDOF AS BEING ACCEPTED; SO I CHANGED ITS FREQ WITHOUT ISSUING A DSCNT CLRNC TO CROSS BUF VOR AT 11000 FT WHICH IS THE SOP. MY ACTIONS OF NOT ENSURING THAT DATA BLOCK AND ISSUED CLRNCS OF ACFT #1 WERE CONSISTENT CONTRIBUTED TO A SUBSEQUENT LACK OF SEPARATION. THE IMPORTANCE OF FOLLOWING THROUGH TO ENSURE CLRNCS REFLECT FLT DATA CANNOT BE OVERSTRESSED.