ARTCC CTLR CLIMBED AN MLG ABOVE HIS SECTOR ALT LIMITS WITHOUT COORD OR HANDOFF AND CREATED LESS THAN STANDARD SEPARATION WITH AN LGT.

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I INADVERTENTLY CLRD MLG X TO FILED ALT OF FL350 INSTEAD OF THE TOP OF MY ALT STRATUM; FL230. I HANDED OFF MLG X TO HIGH ALT SECTOR 91 AND WORKED ON 2 OTHER SEP PROBS AND TALKED TO SEVERAL OTHER ACFT. SEEING THAT MLG X WAS CLBING OUT OF FL240; I BELIEVED THAT I MUST HAVE CHANGED IT TO HIGH ALT'S FREQ; AND THEN DROPPED THE DATA BLOCK ON MLG X. MLG X CALLED APPROX 5-10 MINS LATER ADVISING HE WAS LEVEL AT FL350. BELIEVING MLG X CAME BACK TO MY FREQ BY MISTAKE; I CHANGED HIM TO HIGH ALT'S FREQ. I LATER FOUND OUT THAT SEP WAS LOST BTWN MLG X AND AN LGT Y AT FL330; AND ALSO BY LISTENING TO THE TAPES THAT I HAD CLRD MLG X TO FL350. ACFT DID NOT TAKE EVASIVE ACTION; BUT ULTRA-HIGH CTLR TURNED THE LGT Y AWAY FROM MLG X. CLOSEST PROX WAS ABOUT 3.9 NM AND 900' AT 33900'. SUPPLEMENTAL INFORMATION FROM ACN 80593: WHEN WE WERE TOLD ABOUT THE ALT ALERT; I SAW THE TFC BEFORE HE TOLD US. IT SEEMS THE DEP CTLR WROTE DOWN FL230 BUT SAID FL350. THEN; TO MAKE MATTERS WORSE; HE FORGOT TO HAND US OFF. SUPPLEMENTAL INFO FROM ACN 80699: AT 34500' THE F/O SPOTTED AN EBND AND I BECAME SUSPICIOUS OF A PROB AND TOLD THE CTLR THAT WE WERE LEVELING '350;' DID HE STILL WANT US ON THIS FREQ. HE TOLD US TO SWITCH TO 135.15. AT THIS TIME WE WERE INFORMED OF THE QUALITY ASSURANCE ALERT. THE 2 PROBS WERE THE CTLR NOT FOLLOWING ESTABLISHED PROCS AND THE CAPT NOT DOUBLECHKING WHEN AN UNUSUAL CLRNC WAS RECEIVED.