As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FIRST OFFICER COCKPIT OXYGEN MASK: RIGHT SEAT OXYGEN MASK EMER/TEST KNOB POPPED IN FLIGHT. COULD NOT STOP O2 FLOW. UNPLUGGED MASK. GAINED ACCESS TO AIRCRAFT,REMOVED AND REPLACED CREW OXYGEN MASK AND PERFORMED FUNCTIONAL TEST OPS CHECKS GOOD. PLEASE REFERENCE AMM 35-11-07.