CPR SMT OVERTAKEN BY ACR MLG AT SAME ALT RESULTING IN LESS THAN STANDARD SEPARATION.

Narrative

I WAS WORKING THE D SIDE ON SECTOR 42/46 COMBINED AS ONE SECTOR. SMT X WAS BEING FOLLOWED BY MLG Y BOTH ACFT WITH AN ASSIGNED ALT OF FL370. AT APPROX XA29; I AS D-SIDE ASKED R-SIDE WHAT WE HAD GOING AND ASKED WHY DOES THE A-AREA DO THIS TO US. THE R SIDE ACKNOWLEDGED MY COMMENTS AND ACTED UNCONCERNED. I THOUGHT HE HAD STOPPED MLG Y AT FL330 AND HAD NOT ENTERED AN INTERIM ALT. AT XA32 THE IMMEDIATE ALERT SOUNDED AND THE R-SIDE IMMEDIATELY ISSUED DIVERGING HDGS TO BOTH ACFT. AT THE TIME; WE WERE METERING ARRS AND A LOT OF ENERGY WAS BEING DIVERTED TO MENTAL CALCULATIONS ASSOCIATED WITH MEETING TIMES AT OUTER FIXES IN SECTOR 46. MY RECOMMENDATION IS THAT TRANSFERRING CTLR DO ONE OF 3 THINGS WITH A SIGNIFICANT OVERTAKE SITUATION: ALT STOP ONE OF THE ACFT; ASSIGN DIVERGING HDGS TO ACFT OR CALL RECEIVING CTLR AND ALERT HIM TO THE DEVELOPING SITUATION. CALLBACK CONVERSATION WITH RPTR REVEALED FOLLOWING. RPTR WAS NOT DIRECTLY INVOLVED IN THE SYS ERROR. AFTER INVESTIGATION; IT WAS DETERMINED THAT THE RADAR CTLR IN SECTOR 42/46 WAS ONLY PARTIALLY AT FAULT FOR THIS LOSS OF SEP. PART OF THE ERROR WAS GIVEN TO THE SENDING CTLR FOR NOT DOING ONE OF THE THREE THINGS RECOMMENDED BY RPTR. THE PROX OF TFC WAS ASCERTAINED; AS WELL AS RPTR'S EXPERIENCE LEVEL. RPTR STATED THAT THE DIFFERENCE IN SPD OF THESE 2 ACT WAS 120 KTS; AND THAT THE LOSS OF SEP OCCURRED 3 MINUTES AFTER THE TRANSFER OF CTL TOOK PLACE.