As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI PARKING BRAKE WAS SET & ACFT BEGAN TO ROLL. WHEN PARKING BRAKE WAS RELEASED MAX BRAKING OCCURRED. RETURNED TO GATE WITH NORMAL BRAKING UNTIL NR 2 ENG SHUTDOWN, LOSS OF ALL BRAKING FOR ABOUT 2 SECONDS. AFTER ACFT WAS CHOCKED & ENG NR 1 SHUTDOWN LOSS OF BRAKING OCCURRED AGAIN. REPLACED PARKING BRAKE SELECTOR VLV IAW A320 AMM 32-45-51.