LESS THAN STANDARD SEPARATION WHEN ACR-WDB OVERTAKES ACR-MLG DURING CLIMBOUT.

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AT 300' HDG 255 DEGS; FIRST VECTOR AT 2000' TO 180 DEGS; SECOND AT 3000' TO 120 DEGS; LAST CLRNC BEFORE INCIDENT AT 4000'; 'CLRED DIRECT WOODSTOWN MAINTAIN 6000'.' ABOUT 5000' WHILE TURNING E I SPOTTED ANOTHER ACFT (MLG Y) 2 MI AHEAD AT 1000' ABOVE. I IMMEDIATELY REDUCED MY CLB RATE TO PASS BELOW AND BEHIND THE OTHER ACFT. ABOUT 5500' I WAS TOLD BY DEP CTL OR WASH CENTER TO MAINTAIN 5000' (WHICH I DID); ALTHOUGH I HAD ALREADY ALTERED MY FLT PATH SO AS TO PASS CLR OF THE OTHER ACFT. OUR CLOSEST POINT WAS ABOUT 1/2 MI AND 500' ALT DIFFERENCE. EITHER ATC/DEP CTL CLRED BOTH ACFT TO THE SAME ALT; OR ONE OF THE FLT CREWS MISUNDERSTOOD THEIR CLRNC. THERE ALSO MIGHT HAVE BEEN SOME CONFUSION ON HDOF FROM PHL DEP CTL TO WASH CENTER. I DO NOT KNOW IF THERE WERE ANY ACFT WITH SIMILAR NAMES OR NUMBERS IN THE AREA. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR MADE A RPT TO COMPANY CONCERNING THIS APPARENT LOSS OF SEP. HE HAS NOT RECEIVED WORD YET ON THE FINDINGS OF FAA'S INVESTIGATION. HE STATED THAT THE OTHER ACFT WAS ON THE SAME TRACK AS HIS ACFT AND THAT THEY WERE SLOWLY OVERTAKING THE PRECEDING ACFT. WHEN ASKED ABOUT HIS SPECULATION ABOUT ONE OF THE FLT CREWS TAKING THE WRONG ALT; HE SAID THAT HE ADDED THAT TO HIS RPT ONLY BECAUSE THAT IS ALWAYS A POSSIBILITY. HE STILL THINKS THAT THEIR CLRNC WAS DIRECT OOD; MAINTAIN 6000'.