A ZMP ARTCC RADAR CTLR IMMEDIATELY REALIZED A MISTAKE IN ISSUING A CLRNC TO A C182 UP TO 8000 FT; WHICH WAS OCCUPIED BY B1900; AND RECLRED THE ACFT TO 7000 FT. THE XMISSION WAS BLOCKED AND THE C182 CONTINUED CLB RESULTING IN A LOSS OF SEPARATION.

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ACFT X; MSP TO SPF CHKED ON AT 6000 FT. ACFT Y CHKED ON SHORTLY AFTER AT 8000 FT. ACFT X REQUESTED 8000 FT. I ISSUED 8000 FT; IMMEDIATELY REISSUED 7000 FT; ADVISED OVERTAKING TFC AT 8000 FT. I THEN ISSUED VFR TFC ACFT X COULD CLB THROUGH. PLT ACKNOWLEDGED WITH ROGER; LOOKING. CONFLICT ALERT ACTIVATED AS ACFT X CLBED THROUGH 7300 FT. I TOLD ACFT X TO CHK ALT AND ALTIMETER; ASSIGNED ALT 7000 FT; RWF ALTIMETER 2992. NO RESPONSE; SO REPEATED MY XMISSION. PLT ADVISED HE HAD READ BACK 8000 FT; BUT WOULD DSND TO 7000 FT. CONTRIBUTING FACTORS: NON STANDARD PHRASEOLOGY -- I TOLD PLT TO MAINTAIN 7000 FT; BUT DID NOT USE 'AMEND ALT' WHICH I ALMOST ALWAYS DO. ALSO; AFTER ASSIGNING AND AMENDING ALT I ISSUED IFR AND VFR TFC; MAY BE INFO OVERLOAD. ACFT X THOUGHT HE READ BACK 8000 FT; BUT IT WAS NOT ON TAPE. PLT MAY HAVE KEYED UP; EARLIER DURING MY XMISSION; BUT NO EVIDENCE FOUND ON TAPE RECORDING. CORRECTIVE ACTION: I SHOULD HAVE ASKED FOR AN ALT READBACK. WHEN PLT ROGERS; THAT PUTS ONUS ON HIM OR HER TO HAVE CORRECT CLRNC INFO. HOWEVER; CHK AND DOUBLE-CHKS WOULD HAVE AVERTED A PLTDEV. WE NEED TO BE ON SAME PAGE; AND I SHOULD HAVE QUESTIONED WHETHER WE REALLY WERE. SUPPLEMENTAL INFO FROM ACN 629571: I'M AN ATP PLT WITH 6700 HRS FLT TIME AND AN INST FLT INSTRUCTOR WITH APPROX 2800 HRS OF DUAL GIVEN. I ALSO HAVE 20+ YRS IN THE FAA WORKING AS AN AIR TFC CTLR AND MORE RECENTLY AS AN AREA SUPVR. WE WERE ON AN IFR FLT FROM LVN TO SPF. I WAS PROVIDING FLT INSTRUCTION TO ANOTHER PLT; WITH 2 PAX IN THE REAR SEATS. THE MAKEUP OF THESE OCCUPANTS IS SIGNIFICANT INFO. IN THE REAR SEAT THERE WAS AN OPS MGR AND AN AIR TFC CTLR; BOTH FROM ZMP. IN THE FRONT SEAT; RECEIVING DUAL INSTRUCTION; WAS AN AREA SUPVR; AND MYSELF; ALSO AN AREA SUPVR; BOTH FROM ZMP. OF THE 4 OCCUPANTS; 3 WERE INST-RATED PLTS. WE WERE ALL WEARING HEADSETS AND LISTENING TO ATC; MAKING NOTE OF THE SVC BEING PROVIDED. WE WERE WBOUND AT 6000 FT; WHEN PF REQUESTED 8000 FT. THE CTLR CLRED US UP TO 8000 FT; PF RESPONDED WITH 'LEAVING 6000 FT FOR 8000 FT; ACFT X.' WHEN HE LET UP ON THE MIKE BUTTON; THE CTLR WAS GIVING US VFR TFC AT APPROX 2 O'CLOCK POS; 5 MI; 6500 FT; SWBOUND. PF ACKNOWLEDGED WITH 'ROGER; LOOKING FOR THE TFC.' ALL 4 OF US STARTED LOOKING FOR THE VFR TFC. WHILE CLBING THROUGH 7500 FT; THE CTLR TOLD US TO CHK ALT AND ALTIMETER SETTING; AND THAT WE WERE ONLY CLRED TO 7000 FT. PF IMMEDIATELY RESPONDED BY TELLING THE CTLR THAT WE WERE CLRED UP TO 8000 FT; AND THAT HE READ IT BACK TO HIM; AND DOES HE NOW WANT US TO GO BACK DOWN TO 7000 FT. THE CTLR TOLD US TO DSND AND MAINTAIN 7000 FT. WE DSNDED AND RPTED LEVEL WITHIN 15 SECONDS. SEPARATION WAS LOST BTWN OUR ACFT AND A BE1900D OVERTAKING US AT 8000 FT. FROM THE FAA SIDE AND WHAT SHOWS UP ON THE RECORDED TAPE IS THE FOLLOWING: THE CTLR CLRED US UP TO 8000 FT; PAUSED; THEN RECLRED US TO MAINTAIN 7000 FT; THEN ISSUED THE OVERTAKING TFC AT 8000 FT; THEN ISSUED VFR TFC AT APPROX 2 O'CLOCK POS; 5 MI; 6500 FT; SWBOUND; ALL IN ONE XMISSION. THE CTLR THEN TOOK OUR LAST XMISSION OF 'ROGER; LOOKING FOR THE TFC;' AS AN ACKNOWLEDGEMENT OR READBACK TO HIS ENTIRE XMISSION. WHAT APPEARS TO HAVE HAPPENED; IS THAT THE CTLR CLRED US UP TO 8000 FT; THEN PAUSED; AT WHICH TIME PF STARTED XMITTING WITH THE READBACK. WITH BOTH OF US XMITTING; NEITHER ONE RECEIVED THE OTHER'S XMISSION. THE RECORDED TAPE AT ZMP ONLY RECORDED THE CTR CTLR'S XMISSION; AND NOTHING ELSE. AFTER DOING SOME RESEARCH; I FOUND THAT WHEN A CTLR IS XMITTING; THE TAPE ONLY RECORDS WHAT THE CTLR SAYS; AND NOTHING THAT A PLT OR PLTS MAY BE XMITTING AT THE TIME. OUT IN THE SECTOR; OTHER AIRPLANES WILL HEAR THE GARBLED SOUND WHEN A STEPPED-ON XMISSION OCCURS; BUT NONE OF THAT WILL SHOW UP ON THE RECORDED TAPE; IF THE CTLR HAS THEIR MIKE KEYED. I BELIEVE THIS OCCURRENCE TOOK PLACE DUE TO AN EQUIP LIMITATION; THAT DOESN'T ALLOW EITHER PARTY; TO BE AWARE OF OR HAVE KNOWLEDGE THAT THE XMISSIONS WERE NEVER RECEIVED BY THE OTHER PARTY. I SEE THIS AS A RARE OCCURRENCE; THOUGH ONE THAT WILL PROBABLYREPEAT ITSELF IN THE FUTURE.