MLG DESCENDED TO SAME ALT AS LTT WHO WAS FOLLOWING AND FASTER. ADJACENT ARTCC HAD LESS THAN STANDARD SEPARATION DUE TO NO HANDOFF FROM ZID CTLR.

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THE PROB AROSE FROM A FASTER LTT Y ACFT BEHIND A SLOWER MLG X. THE FASTER WAS DSNDING BELOW THE SLOWER ACFT; WHICH WAS ACCOMPLISHED WITH SEP. BOTH ACFT PUT ON THE NEXT CTLR; BUT THE SECOND (FASTER) ACFT WAS TURNED OVER (SWITCHED) W/O A HDOF. THE NEXT CTLR DSNDED THE FIRST (SLOWER) ACFT DOWN. THEREFORE; THE CONFLICT OCCURRED. I DON'T KNOW IF THE NEXT CTLR REALIZED THAT THE FASTER ACFT WAS ON HIS FREQ AND LOWER THAN THE FIRST. THE FAILURE TO MAKE A HDOF WAS A MISTAKE ON MY PART. THE ONLY WAY TO KEEP THIS FROM HAPPENING BESIDE COMPLETE CTLR AWARENESS IS A POSSIBLE COMPUTER UPDATE TO MAKE SURE ALL HDOFS AUTOMATICALLY HDOF BY A CERTAIN POINT. THIS WOULD MEAN THAT EVEN ACFT WITH A CARROT OVER THE CALL SIGN WOULD AUTOMATICALLY HDOF. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: CALLBACK MADE TO RPTR TO DETERMINE THE TYPE ACFT INVOLVED. RPTR INDICATED THAT THE INCIDENT OCCURRED BTWN ZID AND ZAU ARTCC'S. RPTR SAYS HE THOUGHT THE LTT HAD BEEN HANDED OFF AND GAVE IT A FREQ CHANGE. ZAU CTLR APPARENTLY DIDN'T SEE THE LIMITED DATA BLOCK AND DIDN'T KNOW THE LTT WAS IN HIS AIRSPACE. RPTR HAD AN ASSISTANT CTLR WHO APPARENTLY DIDN'T SEE THE INCIDENT TAKING PLACE. PROX OF ACFT PLACED THE INCIDENT AS A MINOR INFRINGEMENT.