ZFW CTLR EXPERIENCED OPERROR AT APPROX FL330 WHEN ACFT INCORRECT READBACK WAS MISSED AND CLB THROUGH OCCUPIED ALT INITIATED.

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B737 INCORRECTLY READ BACK ASSIGNED ALT. EVEN AFTER ISSUING TFC; THE B737 CONTINUED TO CLB. B737 RPTED ON FREQ AND ASKED ABOUT RIDE CONDITIONS AND REQUESTED FL400. I TOLD ACR X IT WOULD BE 1 1/2 MINS BEFORE A CLB COULD BE ISSUED AND TO EXPECT HIGHER. DURING THIS TIME I DECOMBINED SECTORS AND WAS IN THE PROCESS OF SETTING MY MAP FOR HIGH ALT ONLY WHEN I ISSUED A CLRNC FOR ACR X TO CLB TO FL320. MY D-SIDE WAS OFF ON THE LINE COORDINATING A POINTOUT WHICH ALSO CAPTURED MY ATTN WHILE ACR X WAS READING BACK THEIR CLRNC. I APPLIED MERGING TARGET PROCS BY ISSUING TFC TO BOTH MD80 AND TO ACR X. WHILE THE ACFT WERE STILL VERTICALLY SEPARATED AND 20 MI APART; ACR X QUESTIONED NOTHING. ACR X RPTED ACR Y IN SIGHT. THEY WERE STILL VERTICALLY SEPARATED. I TOLD ACR X TO EXPECT A HIGHER ALT WHEN CLR OF TFC. AN ACFT ASKED TO VERIFY CLB CLRNC TO FL380. THE VOICE SEEMED SIMILAR TO THAT OF ACR X. I ASKED ACR X TO SAY AGAIN. AN ACFT WITHOUT IDENTING THEMSELVES AGAIN ASKED TO VERIFY CLB CLRNC TO FL380. I TOLD ACR X TO MAINTAIN FL320. SEPARATION WAS LOST AFTER THE 2 ACFT PASSED. CLOSEST PROX 2.5 MI 800 FT.