CPR X CLB THROUGH OCCUPIED ALT HAD LTSS FROM ACR Y. SYS ERROR. POTENTIAL CONFLICT.

Narrative

I WAS CTLR IN CHARGE OF THE OZARK AREA IN ZKC. RADAR CTLR; A CTLR UNDER MY SUPERVISION; HAD A MISSED READBACK ERROR THAT RESULTED IN A LOSS OF SEPARATION. THE CLOSEST POINT WAS 0.7 LATERAL AND 0 FT ALT. SUPPLEMENTAL INFO FROM ACN 212922: CPR X WAS AT 10000 FT REQUESTING 14000 FT. I THEN ISSUED 14000 AND THEN LATER ATTEMPTED TO RECLR HIM TO 12000 FOR ACR Y AT 13000 FT LEVEL. WHEN I ISSUED THE CLRNC TO 12000; ANOTHER ACFT WAS XMITTING AT THE SAME TIME AND AFTER I UNKEYED; I HEARD THE END OF HIS XMISSION AND THOUGHT IT WAS THE READBACK FROM CPR X. SUPPLEMENTAL INFO FROM ACN 213632: CPR X WAS CLRED TO CLB FROM 10000 TO 14000 BY ZKC. AS WE PASSED 13000; WE PASSED WITHIN ABOUT 1/8 MI OF AN ACR Y WHO WAS NNEBOUND; TALKING TO SAME CTLR. CTLR: 'CPR X YOU WE TOLD TO STOP AT 12000!' CPR X: 'NEGATIVE; SIR.' CTLR 'YES; YOU WERE! YOU ACKNOWLEDGED THE XMISSION!' CPR Y 'NEGATIVE; SIR.' WE LATER CALLED ZKC; AFTER THEY HAD REPLAYED THE TAPE. THE CTLR'S XMISSION; TELLING US TO STOP THE CLB HAD BEEN BLOCKED (OR SO WE WERE TOLD. WE NEVER HEARD IT OR ACKNOWLEDGED).