B737 FLIGHT CREW REPORTS GOING OFF COURSE ON THE OBRLN1 DEPARTURE FROM CLE AFTER PASSING DJB FOR UNKNOWN REASONS.

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ON CLBOUT FROM CLEVELAND AFTER GETTING RADAR VECTORS NW OF THE ARPT; ATC ISSUED A CLRNC DIRECT TO DJB. AS PF; I LINE SELECTED DJB TO THE TOP OF THE LEGS PAGE; HIT EXECUTE; AND HIT LNAV. I CHKED THAT LNAV ENGAGED; AND WE PROCEEDED TO DJB. AFTER A FEW MINS WE WERE HANDED OFF TO ZOB. A FEW MINS LATER CTR ASKED US IF WE WERE PROCEEDING TO FDY. WE LOOKED DOWN AT THE FMC AND SAW THAT WE WERE FLYING A 'RADAR VECTOR' SEGMENT ON THE LEGS PAGE. WE REPLIED THAT WE WERE FLYING A VECTOR. CTR RESPONDED WITH A DIRECT CLRNC TO FDY. I ENTERED FDY AT THE TOP OF THE LEGS PAGE AND WE PROCEEDED TOWARD FDY. WE DON'T KNOW HOW A RADAR VECTOR SEGMENT ENTERED OUR FLT PLAN ON THE LEGS PAGE; AS IT WAS NOT THERE ON INITIAL PROGRAMMING; AND IT WAS NOT POSSIBLE TO ENTER ONE MANUALLY. THE AUTOPLT NEVER LEFT LNAV MODE AFTER MY INITIAL EXECUTION. IT SEEMED LIKE SOME KIND OF FMS ERROR; BUT WE COULDN'T FIGURE OUT HOW IT WOULD HAPPEN. I DON'T KNOW HOW I COULD HAVE MIS-PROGRAMMED THE FMC THIS WAY; AS THERE WAS NO WAY TO INSERT A RADAR VECTOR INTO THE LEGS; NOR WAS THERE A RADAR VECTOR SEGMENT ANYWHERE IN THE ORIGINAL SID. PERHAPS THERE IS A SOFTWARE GLITCH. CALLBACK CONVERSATION WITH RPTR ACN #809542 REVEALED THE FOLLOWING INFO: THIS RPTR IS POSITIVE THAT THE OBRLN1 DEP WAS CORRECTLY LOADED ALONG WITH THE CORRECT TRANSITION. THERE WERE NO RTE DISCONTINUITIES AND THE LEGS PAGE DID NOT HAVE A VECTOR SEGMENT. AFTER XING DJB; THEY WERE QUERIED BY ATC; WHICH WAS THE FIRST INDICATION OF A PROB.