PAX AND FLT ATTENDANT ABOARD B757 SUSTAIN MINOR INJURIES WHEN PARKING BRAKE APPLICATION FAILS AND ABRUPT ADDITIONAL STOP MADE AFTER RESULTING ACFT MOVEMENT.

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WE PARKED. I SET THE PARKING BRAKE; TESTED PARKING BRAKE HANDLE SECURITY (PUSHED THE HANDLE); OBSERVED THE PARKING BRAKE LIGHT AND NORMAL BRAKE PRESSURE. I ANNOUNCED 'BRAKE SET; PRESSURE NORMAL' AND DIRECTED THE FO TO SHUT DOWN THE R ENG. I BEGAN NORMAL AFTER PARKING DUTIES BUT AFTER REPOSITIONING ONLY 2 SWITCHES (SEATBELT SIGNS AND EMER EXIT LIGHTS); I NOTICED ACFT MOVEMENT AND APPLIED BRAKES. THE STOP WAS ABRUPT. I WAS SIMULTANEOUSLY RELIEVED THAT I STOPPED THE ACFT WITHOUT SIGNIFICANT MOVEMENT AND CONCERNED ABOUT POSSIBLE INJURIES; AS PEOPLE ARE UP THE INSTANT THE SIGN IS TURNED OFF IF NOT BEFORE. I NOTED THAT THE PARKING BRAKE LIGHT WAS NO LONGER ILLUMINATED AND THE HANDLE WAS NOT IN THE 'SET' POS ALTHOUGH I DON'T KNOW IF THIS RESULTED FROM THE MANUAL BRAKE APPLICATION USED TO STOP THE ACFT SINCE SIGNIFICANT BRAKE APPLICATION RELEASES THE PARKING BRAKE. I AGAIN SET THE PARKING BRAKE; ALBEIT WITH SOME AWKWARDNESS AS I WAS UNABLE TO ACHIEVE THE NORMAL ENGAGEMENT FEEL OF THE PARKING BRAKE HANDLE. HOWEVER; THE PARKING BRAKE LIGHT REMAINED ILLUMINATED; PRESSURE WAS NORMAL AND THE HANDLE REMAINED IN PLACE WHEN TESTED FOR SECURITY. I CHKED WITH THE FLT ATTENDANTS AND LEARNED OF 1 PAX INJURY AND LATER LEARNED OF INJURIES TO 2 FLT ATTENDANTS. I HAD THE FO CALL FOR PARAMEDICS. THE FO RECOMMENDED STARTING THE APU AND SHUTTING DOWN THE L ENG; WHICH WE DID. I SPOKE WITH RAMP PERSONNEL VIA THE HEADSET AND THEY CONNECTED THE TOW BAR AND TUG TO REPOS THE ACFT BACK TO THE STOP LINE. I WAS STILL UNCOMFORTABLE WITH THE PARKING BRAKE SO WHEN WE CONDUCTED THE PARKING CHKLIST I CYCLED THE PARKING BRAKE WITH THE SAME RESULT -- PROPER INDICATIONS BUT LACK OF NORMAL HANDLE FEEL UPON ENGAGEMENT. MOMENTS LATER; RAMP ADVISED THAT THE L ENG MAY HAVE CONTACTED THE JETBRIDGE. AFTER A SIGNIFICANT DELAY; LCL PERSONNEL ELABORATED THAT THE JETBRIDGE WOULD NOT BE BROUGHT TO THE ACFT (AND PARAMEDICS WOULD NOT BOARD) UNTIL PICTURES HAD BEEN TAKEN. I DECLARED A MEDICAL EMER AND INSISTED THAT PARAMEDICS BE ALLOWED TO BOARD. THE LCL OPS REITERATED THAT THE JETBRIDGE WOULD NOT BE MOVED UNTIL PICTURES WERE TAKEN BUT THAT PARAMEDICS COULD BOARD VIA EXTERNAL STAIRS. PARAMEDICS BOARDED AT DOOR 3L. LATER THE JETBRIDGE WAS REPOSITIONED TO DOOR 2L. THE PAX WAS APPARENTLY ALRIGHT AND WALKED OFF THE AIRPLANE. 1 FLT ATTENDANT CLAIMED SHE WOULD BE FINE. PARAMEDICS ATTENDED TO THE OTHER FLT ATTENDANT. DUE TO CONFLICTING STATEMENTS; I DID NOT GET A CLEAR UNDERSTANDING OF HER CONDITION. AFTER ALL PAX AND CREW WERE ACCOMMODATED; THE FO AND I WENT TO THE RAMP. THE DISTANCE FROM THE B757 STOP MARK WAS FAR GREATER THAN WE HAD IMAGINED. I STEPPED OFF THE DISTANCE TO ESTIMATE 21 FT! NEITHER I NOR MY FO CAN ACCOUNT FOR THE TIME REQUIRED FOR THAT MUCH ACFT MOVEMENT BTWN INITIAL PARKING BRAKE APPLICATION AND THE ABRUPT STOP. DURING DISCUSSION WITH THE FO; I LEARNED HE HAD ALSO APPLIED THE BRAKES; APPARENTLY SIMULTANEOUSLY WITH MY EFFORT. OBVIOUSLY; THE ACFT HAD NOT YET BEEN CHOCKED. THIS IS CONSISTENT WITH COMPANY PROCS SINCE CHOCKING THE ACFT SERVES AS A SIGNAL THAT IT IS SAFE FOR PERSONNEL TO APPROACH THE R SIDE; SO CHOCKING IS NOT NORMALLY ACCOMPLISHED UNTIL AFTER THE R ENG HAS SPOOLED DOWN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE FO HAD NO ADDITIONAL INFO REGARDING THE CAUSE OF THE INCIDENT. ANALYST WAS UNABLE TO CONTACT THE CAPT.